Organometallic chemistry of transition metal - group 13

1

Organometallic Chemistry of Transition

Metal – Group 13 Complexes and

Metal-Organic Precursor Synthesis for

ALD Cobalt Oxide Thin Films

Cumulative Dissertation

Jiyeon Kim

Part I

Organometallic Synthesis of Transition

Metal – Group 13 Complexes

Part II

Precursor Synthesis and Atomic Layer

Deposition of Cobalt Oxide

Dissertation

Faculty of Chemistry and Biochemistry

Ruhr-University Bochum

Submitted by

Jiyeon Kim, M.Sc.

February 2017

This work has been performed in the time between May 2013 and January 2017 under

supervision of Prof. Roland A. Fischer and Prof. Anjana Devi at the Chair of Inorganic

Chemistry II – Organomatallics & Materials Chemistry of Ruhr-University Bochum, Germany.

1st referee: Prof. Dr. Roland A. Fischer

2nd referee: Prof. Dr. Anjana Devi

Herein I declare that I have written the corresponding cumulative thesis myself independently

without any other help or source which are not specifically and explicitly marked or authorized

in this dissertation. Furthermore, I declare that I have not applied to any other review procedures

or submitted this cumulative thesis in the same, similar or different form to another faculty or

university as a dissertation.

Jiyeon Kim, February 2017

Acknowledgement

I am deeply grateful to many people who supported me with every meaningful way to manage

this work. Amongst, I sincerely appreciate my supervisor Prof. Roland A. Fischer for his

support and generosity for giving the great opportunity to be at AC II. With no doubt, it was a

dream to work in organometallics regardless of the frustrating outcome.

I wish to express my gratitude to Prof. Anjana Devi who is the supervisor of the ALD part of

my thesis. I appreciate your efforts for giving me guidance from totally different field to another.

I was given the inspiration as well as the motivation of learning about materials science in very

productive environment.

I wish to thank to Christian Gemel for his supervision also scientific support.

I am thankful to Prof. Markku Leskelä from University of Helsinki in Finland for providing me

the opportunity to learn atomic layer deposition from one of the pioneering group in the ALD

field.

I would like to thank Dr, Mariusz Molon, Dr. Arik Puls, Hung Banh who provided me a

guidance to establish and settle down at OM group at the beginning.

I am thankful to Dr. Andreas Schneemann, Suttipong Wannapaiboon, Dr. Clarissa Kroll, Dr.

Sunja Kim for welcoming me and giving the introduction of Ruhrgebiet at the beginning.

I would like to thank Dr. Markus Halbherr, Dr. Arik Puls, Dr. Mariusz Molon, Dr. Kerstin

Freitag, Hung Banh, Jana Weßing and Manuela Winter for the introduction and guidance of

single crystal X-ray diffraction and synthetic skills in the lab.

I am very thankful to Tomi Iivonen from University of Helsinki in Finland who offered me an

excellent supervision and fun while learning the ALD process including the maintenance of F-

120.

I would like to thank the OM group and the CVD group for the scientific support and advise as

well as to the whole ACII including the former members for providing me the great and

comfortable working environment. Especially, thanks to all the office member at NC 2/27 who

always brought interesting conversation topic to drag me out of work.

I would like to thank Prof. Radim Beranek for successfully instructing the 4G Photocat EU

project as a leader and organizing the interesting meetings in different countries which allowed

me to broaden my knowledge on different field. Also, his contribution of photoelectrochemical

catalysis expertise on my work.

I would like to thank the New York and Boston crew, Dr. Christian Wiktor, Dr. Andreas

Schneemann, Dr. Wenhua Zhang, Jana Weßing, Inke Hante who joined the ACS fall meeting

on 2015, especially Wenhua Zhang and Inke Hante for having girls’ night out in Boston and

Jana Weßing and Andreas Schneemann for having together a wonderful time during the round

trip in the US and Canada afterwards.

I thank Dr. Clarissa Kroll who joined me to the ICOMC 2014 in Sapporo, Japan and during the

travel to Tokyo and Kyoto afterwards.

I would like to thank Dr. Mariusz Molon, Dr. Arik Benjamin Puls and Hung Banh for their

guidance at the beginning to help me settle down in the group and learn quickly to handle the

air sensitive reactions.

I would like to thank Inke Hante or Schwedler for her friendship and having an awesome chat

in the chair as well as outside of the chair. Thanks to Jana Weßing for hanging out together at

scientific and non-scientific meetings accompanied with beer. I am thankful to Sarah Karle

having a short break together every day at 02 in front of NC. Thanks to Stefan Cwik for his

guidance in CVD as well as common humor. Thanks to Alexander Sadlo for introducing

Bouldering which I still cannot manage to do well but it was fun. I would like to thank all the

CVD group for their help and welcoming me as a CVD group.

I would like to thank Dr. Andreas Schneemann and Richard O’Donoghue, Dr. Steven Hughes,

Kathryn Poole for generously proof reading my English during my study.

I would like to thank Sabine Pankau who is a wonderful colleague always being supportive

with non-scientific issues even though it was not her task.

I would like to thank Niklas Stegmann for his assistance on the synthesis in the lab during the

in-depth practical.

I express my special thanks to my friends Meike Stiepel and Christian Groß and Andreas

Schneemann for their friendship and spending plenty of time together that I could avoid feeling

home sick. The chemistry what we did together was the most fun during my PhD while drinking

and brewing Panda Gom Pale Ale.

Finally, I wish to thank from the bottom of my heart to Dr. Andreas Schneemann for his

unconditional love and support and made it possible for in many ways.

“I am one of those who think, like Nobel, that humanity will draw more good than evil from

new discoveries.”

Marie Curie

Contents

Part 1 Organometallic Synthesis of Transition Metal – Group 13 Complexes

1 Motivation .......................................................................................................................................1

List of Abbreviation .............................................................................................................................2

2 Introduction .....................................................................................................................................3

2.1 Organometallic Chemistry .........................................................................................................3

2.2 Historic Development and Significance of Organometallic Chemistry.........................................3

2.3 Discovery of the Low-Valent Group 13 Organyls and Chronological Development of Their

Synthesis ....................................................................................................................................... 10

2.4 Coordination chemistry of ECp* toward transition metals ....................................................... 12

2.5 Redox Chemistry of Transition Metal Group 13 Complexes...................................................... 16

3. References ................................................................................................................................ 19

3 Oxidation of Ni-ECp* Complexes: Stable Open-Shell NiI Cations [Ni(ECp*)n(PPh3)4−n]+ (n = 2, 4; E = Al,

Ga).................................................................................................................................................... 24

3.1 Abstract ...................................................................................................................................... 24

3.2 Introduction ............................................................................................................................ 24

3.3 Result and Discussion .............................................................................................................. 26

3.4 Conclusion .............................................................................................................................. 29

3.6 Experimental Section .................................................................................................................. 33

3.6.1 General Comments............................................................................................................... 33

3.6.2 Synthetic Procedures ............................................................................................................ 34

3.6.3 Spectroscopic and crystallographic data ............................................................................... 36

4 References ................................................................................................................................. 47

4. Organoaluminum Palladium Complex via Reductive Elimination ................................................... 49

4.1 Abstract .................................................................................................................................. 49

4.2 Introduction ............................................................................................................................ 49

4.3 Result and Discussion .............................................................................................................. 50

4.4 Conclusion .............................................................................................................................. 53

4.5 Experimental Section............................................................................................................... 55

4.5.1 General Comments ........................................................................................................... 55

4.5.2 Synthetic procedure ......................................................................................................... 55

4.5.3 Spectroscopic, Spectrometric, Crystallographic Data......................................................... 56

5. References ................................................................................................................................ 62

List of Abbreviation ........................................................................................................................... 64

5 General Introduction ...................................................................................................................... 67

5.1 General Introduction ............................................................................................................... 67

Physical Vapor Deposition ......................................................................................................... 68

Chemical Vapor Deposition ....................................................................................................... 68

5.2 Atomic Layer Deposition ......................................................................................................... 69

5.3 ALD of metal oxides thin films ................................................................................................. 72

5.3.1 Precursors ........................................................................................................................ 72

5.3.2 Transition metal oxides and cobalt ................................................................................... 80

6. References ................................................................................................................................ 82

6. Low temperature atomic layer deposition of cobalt oxide as an effective catalyst layer for

photoelectrochemical water splitting devices ................................................................................... 88

6.1 Abstract .................................................................................................................................. 88

6.2 Introduction ............................................................................................................................ 89

6.3 Results and Discussion............................................................................................................. 91

6.3.3 Film Characterization............................................................................................................ 95

6.4 Conclusion and Outlook ........................................................................................................ 102

6.5 Appindex ............................................................................................................................... 102

6.5 Experimental Section............................................................................................................. 107

6.5.1 Precursor synthesis......................................................................................................... 108

6.5.2 Film deposition ............................................................................................................... 109

6.5.3 Film characterization ...................................................................................................... 109

6.5.4 Photoelectrochemistry ................................................................................................... 111

6.6 References ............................................................................................................................ 112

7. Homoleptic all nitrogen coordinated bis-guanidinato cobalt (II) complex: Volatile and thermally

stable precursors suitable for ALD/CVD ........................................................................................... 136

7.1 Abstract ................................................................................................................................ 136

7.2 Introduction .......................................................................................................................... 136

7.3 Result and Discussion ............................................................................................................ 139

7.4 Conclusion ............................................................................................................................ 148

7.5 Experimental Section............................................................................................................. 150

7.5.1 General Comments ......................................................................................................... 150

7.5.2 Synthetic Procedure ....................................................................................................... 150

7.5.3 Crystallographic data .......................................................................................................... 152

8. References .............................................................................................................................. 153

Curriculum Vitae ............................................................................................................................. 155

PART 1 Organometallic Synthesis of Transition Metal – Group 13 Complexes

1

1 Motivation

This cumulative thesis consists of two parts whereas Part 1 deals with the synthesis and characterization

of novel organometallic complexes. On the other hand, Part 2 describes the synthesis of new cobalt

precursors for the use in thin film deposition techniques (Part 2 chapter XY) as well as the development

of a ALD process for the preparation of efficient cobalt-oxide thin film photocatalysts.

The driving force for pursuing the first project based on pure organometallic chemistry, was the

preparation of new organometallic complexes with unusual bonding situation and structural features. In

Part 1 chapter 4 the use of reductive elimination as a tool for the preparation of new building blocks and

precursors for metal-rich clusters is explored. These clusters bear potential for a wide range of

applications including catalysis and medical application. In chapter 3 of Part 1 the focus lays on the

preparation of stable open shell NiI species, which are extremely rare and the exploration of these

compounds and in particular the documentation of reliable synthesis conditions can be of extreme

usefulness for future studies.

The second part of the thesis is much closer to application and was embedded in the Photocat-4G

Network. The overall goal of this project was the preparation of thin film devices useful for the

photocatalytic degradation of pollutants in water. As part of my thesis, new precursors were developed

for this project and in close collaboration with the University of Helsinki, we worked on new atomic

layer deposition processes for the preparation of spinel-cobaltoxide thin films, which is are promising

photocatalytic materials.

My role within this project was on the one hand the preparation of known (commercially unavailable)

and novel precursor molecules for the thin film depositions, and additionally, I was during two academic

stays at the university of Helsinki deeply involved in the film depositions as well as characterizations.


1

PART 1 Organometallic Synthesis of Transition Metal –

Group 13 Complexes


2

List of Abbreviation

BAr4F B[C6H3(CF3)2]4

DDP 2-Diisopropylphenylamino-4-diisopropylphenylimino-2-pentene

dvds 1,3-Divinyl-1,1,3,3-tetramethyldisiloxane

COD 1,5-Cyclooctadiene

COT Cyclooctatetraene

Cp Cyclopentadienylanion

CpH 1,3-Cyclopentadiene

Cp* Pentamethylcyclopentadienylanion

Cp*H 1,3-Pentamethylcyclopentadiene

E Group 13 metals

EA Elemental Analysis

Et Ethyl

EIR Monovalent group 13 organyls

Et2O Diethylether

iPr iso-propyl

LIFDI Liquid Injection Field Desorption Ionization

Me Methyl

NHC N-heteocyclic-carbene

Ph Phenyl

Rt Room temperature

TM Transition metals

tBu tert-butyl

tmeda N,N,N’,N’-Tetramethylethylen-1,2-diamine


3

2 Introduction

2.1 Organometallic Chemistry

Organometallic Chemistry describes the chemistry of compounds, which contain at least one

direct carbon to metal bond. This includes all transition metals, earth alkaline and alkaline as

well as lanthanides, actinides, post transition metals and metalloids. The field of organometallic

chemistry has a huge impact on the day-to-day life of millions of people, since organometallic

complexes are used for a wide range of large-scale homogeneously catalyzed reactions as well

as precursors for the preparation of thin films in the semiconductor industry. The influence of

this field was honoured with several Nobel Prizes in chemistry. For instance, for the discovery

of the Grignard Reagent and Metal Catalyzed Hydrogenation for Victor Grignard and Paul

Sabatier in 1912 and the discovery of the Metallocenes by E.O. Fischer and G. Wilkinson in

1973. Also, several Nobel Prizes were awarded for the development of groundbreaking

catalysts based on organometallic compounds (e.g. 1963 for Ziegler-Natta Catalysis, 2001 for

assymetric hydrogenation, 2005 for metal-catalyzed metathesis and 2010 for palladium

catalyzed cross-couplings).

2.2 Historic Development and Significance of Organometallic Chemistry

Figure 2.1: Depiction of the synthesis of one of the first organometallic compounds cacodyl by

Louis Claude Cadet de Gassicourt in 1760.


4

As in many cases in the history of new fields in chemistry, the discovery of organometallic

compounds was a mere serendipity. The first reported man-made organometallic compound is

most likely (As2(CH3)4), or Cacodyl, which was a component of “Cadet’s Fuming Liquid”. This

liquid was prepared in 1760 by Louis Claude Cadet de Gassicourt by the reaction of AsO3 and

potassium acetate. A side product of this reaction is cacodyl oxide. The presence of methyl

radicals, who are bound to the Arsen was later postulated by Robert Bunsen.

Figure 2.2: Schematic of the preparation of Zeise Salt by the reaction of K2PtCl4 in boiling

ethanol.

In 1827 William Zeise discovered the first Olefin Transition Metal-Complex, the so called Zeise

Salt which has the formuly [K[PtCl3(C2H4)]·H2O. This compound was prepared by reacting

PtCl4 in boiling ethanol. In this comlex the platinum is fourfold coordinated, with each chlorine

taking up one coordination site and the C2H4 coordinating to the fourth site with a η2 bond.

However, the real composition and structure remained for a long time under controversial

discussion. The chemist at that time very influential chemist Justus Liebig highly criticized the

assumption by Zeisse that Ethylene is bound within the structure. The ultimate proof for the

presence of Ethylene in this structure was finally given by the chemist Birnbaum in 1868, who

prepared the same compound using Ethylene gas. During the second half of the 19th century the


5

constitution of this compound remained uncertain and was finally resolved in the 1920 with the

development of X-ray diffraction techniques.

Figure 2.3: Depiction of the synthetic route of Edward Frankland towards diethylzinc.

Edward Frankland discovered another milestone compound of historical significance, the very

pyrophoric compound diethyl zinc (Zn(Et)2). It was prepared by the reaction of zinc with

ethyliodide. Due to its reactive nature it has become a very important reactant in organic

chemistry.

Ludwig Mond discovered the first carbonyl compounds in 1890. Ni(CO)4 is an intermediate in

the so called Mond process, which is used for the preparation of highly pure Nickel.

Nickeloxide, NiO reacts with Syngas (H2 and CO), forming impure Ni and H2O. At

temperatures of roughly 50-60 °C the NiCO4 is formed from the prepared impure Nickel.

NiCO4 is a highly volatile gaseous compound and can be deposited as ultrathin pure Nickel

films on substrates or pallets at around 220 °C. Among the carbonyl preparation reactions, this

is the one occurring under the mildest conditions.


6

Figure 2.4: Illustration of the three steps occuring during the Mond process for the preparation

of ultra-pure Nickel

The chemistry of carbonyls was promoted later on by the likes of Walter Hieber and Walter

Reppe. Walter Hieber did a lot of groundbreaking research at the Technical University Munich

since the 1920s and developed among other things the first routes towards Metal Carbonyl

Hydrides, for instance Fe(CO)4H2 or Mn(CO)H5. These hydrides, particularly Co(CO)4H and

Rh(CO)4H are still today important intermediates of the catalysts for the hydroformulation,

which is used for the preparation of Aldehydes from Olefins (Figure 5). Walter Repp on the

other hand worked for the BASF (Badische Soda und Anillin Fabrik) and developed a manifold

of catalytic processes using Ni(CO)4 or Co(CO)4 as catalysts for the hydrocarboxylation of

Olefins and Alkynes using CO as a reagent. The carbonyl chemistry however is not only limited

to large scale industrial reactions, also in nature, so far three active centers of enzymes have

been identified to be metal-carbonyls.


7

Figure 2.5: Scheme of the reaction process of hydroformulation using one of the metal carbonyl

hydrides discovered by Walter Hieber.

A further class of important organometallic compounds are the so called sandwhich complexes.

This class of molecules features usually two arenes bound to a metal center on opposite sites

by a haptic covalent bond. The most famous subclass of these materials are the metallocenes,

which feature two cyclopentadienyl units bound to a metal center. The first metallocene

reported was Ferrocene, which was independently discovered by Kealy and Pauson, as well as

Miller et al. in 1951. Kealy and Pauson were actually trying to prepare Fulvalene from a

cylopentadienyl salt using anhydrous ironchloride as an electron acceptor. The reaction of

Miller et al. featured Cyclopentadiene, iron as well as the oxides of either aluminum, potassium

or molybdenum. Both reactions yielded a product with the sum formula C10H10Fe.


8

Figure 2.6: Depiction of the two different synthetic pathways of Pauson and Kealey (a) and

Miller (b) towards Ferrocene.

In the following year Fischer and Wilkinson determined the structure of the compound and

concentrated on the further development of the metallocenes. Their works demonstrated that

the electrons located on the cyclopentadienyl ring equally contributed to the bonding of the

metal-center between the two aromatic rings, leading to a η5 bond. Fischer and coworkers

furthermore developed analogues compounds for Nickel and Cobalt. Metallocenes and their

derivatives are of significance for polymerization reactions, and are used as Ziegler Natta

Catalysts.


9

Figure 2.7: Depiction of the Singlet-Fischer-Carbenes as well as the Triplet-Schrock-Carbenes

including an example for both classes.

Apart from his research on metallocenes, E.O. Fischer also helped establishing the class of

metal-carbenes, with R. Schrock being another important figure in this field of organometallic

chemistry. In the honor of these two scientists two classes of metallcarbenes are named Fischer

and Schrock Carbenes. The Fischer Carbenes feature high oxidation state metal-centers, usually

use middle and late transition metals and are π-acceptor ligands, while the Schrock Carbenes

consist of low oxidation state metal centers of early transition metals and are usually π-donor

ligands. Apart from these two classes, N-heterocyclic carbenes (NHC) are much more

commonly used, since they are purely spectator ligands, that do not influence the electronic

structure of the metal as heavily as the afore mentioned Fischer and Schrock Carbenes. These

NHC Ligands are of high relevance, in the research towards new catalysts and have also been

established in the chemical industry, e.g. as a part of Grubbs catalysts used for the olefin

methathesis (Figure 8).


10

Figure 2.8: Depiction of the first and second generation Grubbs Catalysts, which both employ

carbenes in their structure.

2.3 Discovery of the Low-Valent Group 13 Organyls and Chronological

Development of Their Synthesis

The exotic chemistry of low valent group 13 organyls EIR (E = Al, Ga, In, Tl) has caught

enormous attention by the organometallic community due to their stability and availability as

ligands in coordination chemistry. The first synthesized low valent group 13 compounds were

InCp and TlCp reported already in 1957 by E. O. Fischer and H. Meister.1-2 Since the synthetic

route of those heavier element containing EIR group 13 organyls is not feasible for the lighter

elements such as aluminum and gallium, the syntheses of AlIR and GaIR were published 34

years later. Schnöckel et al. successfully synthesized [AlCp*]4 in 1991. Reaction of AlCl and

[MgCp2] led to tetrameric [AlCp*]4.3 Two years later in 1993, Schnöckel et al. achieved to

synthesized the related gallium (I) organyls including [GaCp*]6 and its Cp derivatives using the

same synthetic pathway.4 (Scheme 1)


11

Scheme 2.1 Synthesis of ECp*

Thereafter, Jutzi et al. reported an alternative synthetic method which provided more

convenient access to EIR.5-6 The former methods required metastable AlCl and GaCl generated

at harsh conditions e.g. heating to 1000 °C, while the routes provided by Jutzi comprises

reductive elimination of salt in Cp*AlCl2 and Cp*GaI2 employing elemental potassium.

(Scheme 2)

Scheme 2.2 Synthesis of ECp*

Nowadays the most commonly used synthetic method to prepare GaCp* is using metal stable

GaI generated by ultra-sonication in benzene which is a modified procedure of a report by Green

et al. who synthesized in 1990 a different, unrelated GaI species.7 (Scheme 3)

Scheme 2.3 Synthesis of GaCp* (most commomly adopted procedure)


12

In 2012, Ganesamoorthy et al. developed a new large scale synthetic route towards AlCp* via

thermally induced reductive elimination of Cp*H from the organo-aluminum hydride species

Cp*2AlH in an exceptionaly high yield (93 %).8 The reaction of AlCl3 with LiAlH4 in 3:1 molar

ratio leads to Cl2AlH which reacts further with KCp* in Et2O to afford Cp*2AlH. Cp*2AlH

reductively eliminates Cp*H in toluene at 110 °C. (Scheme 4)

Scheme 2.4 Synthesis of AlCp* (improved procedure for large scale synthesis)

Due to the stability as well as the isolobal structure to CO or phosphines, EIR species are

interesting ligands for transition metals in coordination chemistry. This topic will be discussed

more in detail in the next section. (See 2.4)

2.4 Coordination chemistry of ECp* toward transition metals

EIR species are an isolobal analogs of CO or phosphine, they possess two vacant p orbitals

perpendicular E−R axis and one lone pair electron in the orbital. (Figure 9)


13

Figure 2.9 Isolobality of EIR species and CO

Therefore, the interaction between the EIR species and transition metals follows as shown in

Figure 2.

Figure 2.10 Bonding situation in transiton metal-EIR complexes.


14

The synthetic strategy of ECp* transition metal compounds is frequently found in the form of

ligand substitution reactions with labile ligands. The first attempt for synthesizing TM-EIR

complexes was performed using homoleptic TM−carbonyls. However, the strong -donating

properties of ECp* increase the -backdonating properties of carbonyls which prohibits the

further substitution of ligands. Accordingly, labile ligands with weaker -accepting properties

such as olefins were adopted to access homoleptic ECp*−TM complexes. (Scheme 5) In the

case of palladium, the redox reaction takes place at the palladium center transforming one

equivalent of GaICp* to Me2GaIIICp* as a byproduct.

Scheme 2.5 Synthesis of homoleptic TM−ECp* complexes

The homoleptic [M(ECp*)4] complexes are used as molecular building blocks for multi-nuclear

clusters. T. Steinke et al. synthesized homoleptic dimeric clusters including [Pt2(2-

AlCp*)(AlCp*)2] and [Pd2(2-GaCp*)(PPh3)2] by treatment of [M(GaCp*)4] with [M(cod)2]

or [Pd(dvds)3] (cod = 1,5-Cyclooctadiene, dvds = 1,3-Divinyl-1,1,3,3-tetramethyldisiloxane)

and subsequent addition of ECp*.9 (Scheme 6) Heteroleptic dimeric clusters are accessed by

the treatment of [Pd2(dvds)3] or [Pt(cod)2] by 3.0 equiv. of GaCp* and 2.0 equiv. of PMe3.

(Scheme 7)


15

Scheme 2.6 [M(GaCp*)4] as building block for dimeric clusters of the type [MPt(GaCp*)2(-

GaCp*)3].9 Reprinted with permission from Organometallics, 2003, 22 (13), pp 2705–2710.

Copyright (2003) American Chemical Society.

Scheme 2.7 Synthesis of heteroleptic dimeric clusters of the type [M2(GaCp*)3(PMe3)2].10

Reprinted with permission from Dalton Trans., 2014, 43, 3114–3120. Copyright (2014) Royal

Society of Chemistry.

In a similar manner, trimeric homoleptic clusters can be synthesized by controlling the

stoichiometry of ECp*.10-11

Recently, it has been discovered a novel pathway to approach heteroloptic dimeric cluster via

reductive elimination unlike the conventional method by substitution of labile ligand with ECp*.

This will be discussed in chapter 4 as a major discussion of this thesis.

The ECp* containing transition metal complexes are used as well in synthesis of metal-rich

complexes. M. Molon et al synthesized organozinc-rich palladium and platinum clusters.10

(Scheme 8)


16

Treatment of 6.0 equivalents of ZnMe2 and excess of PMe3 with [M(2-GaCp*)3(PMe3)] (M =

Pd or Pt) leads to mononuclear compounds [M(ZnCp*)2(ZnMe2)(PMe3)2].

Scheme 2.8 Synthesis of zinc rich transition metal clusters.10 Reprinted with permission from

Dalton Trans., 2014, 43, 3114–3120. Copyright (2014) Royal Society of Chemistry.

2.5 Redox Chemistry of Transition Metal Group 13 Complexes

The reaction of cationic complexes such as [Ga2Cp*][BAr4F] and [FeCp2][BAr4

F] with ECp*

containing transition metal complexes gives further insight into the redox chemistry of ECp*

species. Treatment of homoleptic complex [M(GaCp*)4] with one equivalent of

[Ga2Cp*][BAr4F] or [FeCp2][BAr4

F] led to the product [MGa(GaCp*)4][BAr4F] (M = Ni or Pt)

whereas 1/3 equiv. of [FeCp2][BAr4F] yielded [(2-Ga)Pt3(GaCp*)6][BAr4

F].12-13


17

Scheme 2.9 Reaction of [M(GaCp*)4] (M = Ni or Pt)with [FeCp2][BAr4F] leading to an

oxidative cleavage of Cp* to form “naked” Ga+ containing complexes.[Buchin 2006, Halbherr

2010] Reprinted with permission from Angew. Chem. Int. Ed. 2006, 45, 5207 –5210 and Angew.

Chem. Int. Ed. 2010, 49, 1878 –1881 Copyright (2006, 2010) Wiley.

Reaction behavior of heteroleptic complex of the type [Ni(ECp*)2(PPh3)2] with [FeCp2][BAr4F]

will be discussed as a major topic of this thesis in chapter 3 in detail.

Aforementioned new synthetic route from aluminum (III) hydride species to AlICp* developed

by C. Ganesamoorthy et. al.8 is an inspiration of redox chemistry of group 13 complexes. Indeed,

hydrides of main group metals are playing a key role in organic synthesis as Lewis acid

catalysis14-21 and hydrogen storage materials22-23 as well as in material chemistry due to its

volatility in chemical vapor deposition techniques 24-27 Moreover, the comprehensive

elucidation of chemical reactivity of hydrides in terms of addition, elimination and redox

reactions has been a goal for inorganic chemical society.28-31 Previous studies of main group

hydride compounds show the unusual stabilization of aluminum with +1 oxidation state via


18

reductive dehalogenation from the aluminum halide species5, 28, 30, 32 and ECp* is remains

arguably the excellent example of those studies due to their exotic chemistry and strong

donating and accepting properties towards transition metal complexes.6

C. Ganesamoorthy et al reported a novel pathway to AlICp* via reductive elimination of Cp*H

from Cp*2AlH while Cp*AlH2 reductively eliminates Cp*H and forms metallic Al0. Both

results provided very important information in terms of not only the final product but also the

type of chemical bonding. Cp*2AlH and Cp*AlH2 lead to the formation of metal-metal bonds

where the aluminum metal is clearly containg metal-metal bonds as well as AlCp* known as

tetrameric complex [AlCp*]4.8 This work was an inspiration of preparing intermetallic

complexes including bonds between transition metals and group 13 metals via intramolecular

reductive elimination. The reaction with aluminum hydride towards transition metal complexes

leading to the formation of TM-Al will be discussed in detail in chapter 4.


19

3. References

1. Fischer, E. O.; Hofmann, H. P., Metall-cyclopentadienyle des Indiums. Angew. Chem.

1957, 69, 639-640.

2. Meister, H., Cyclopentadienyl-thallium. Angew. Chem. 1957, 69, 533-534.

3. Dohmeier, C.; Robl, C.; Tacke, M.; Schnöckel, H., The Tetrameric Aluminum(I)

Compound [{Al(η5-C5Me5)}4]. Angew. Chem., Int. Ed. 1991, 30, 564-565.

4. Loos, D.; Schnöckel, H., (Cyclopentadienyl)-Gallium(I)-Verbindungen. J. Organomet.

Chem. 1993, 463, 37-40.

5. Schulz, S.; Roesky, H. W.; Koch, H. J.; Sheldrick, G. M.; Stalke, D.; Kuhn, A., A Simple

Synthesis of [(Cp*Al)4] and Its Conversion to the Heterocubanes [(Cp*AlSe)4] and

[(Cp*AlTe)4] (Cp* = η5-C5(CH3)5). Angew. Chem., Int. Ed. 1993, 32, 1729-1731.

6. Jutzi, P.; Neumann, B.; Reumann, G.; Schebaum, L. O.; Stammler, H.-G.,

Pentamethylcyclopentadienylindium (Cp*In) as Terminal Ligand in the Chemistry of

Chromium. Organometallics 1999, 18, 2550-2552.

7. Green, M. L. H.; Mountford, P.; Smout, G. J.; Speel, S. R., New synthetic pathways into

the organometallic chemistry of gallium. Polyhedron 1990, 9, 2763-2765.

8. Ganesamoorthy, C.; Loerke, S.; Gemel, C.; Jerabek, P.; Winter, M.; Frenking, G.;

Fischer, R. A., Reductive elimination: a pathway to low-valent aluminium species. Chem.

Commun. 2013, 49, 2858-2860.

9. Gemel, C.; Steinke, T.; Weiss, D.; Cokoja, M.; Winter, M.; Fischer, R. A., [M(GaCp*)4]

(M = Pd, Pt) as Building Blocks for Dimeric Homoleptic Cluster Compounds of the Type

[MPt(GaCp*)5]. Organometallics 2003, 22, 2705-2710.

10. Molon, M.; Gemel, C.; Fischer, R. A., Organogallium- and organozinc-rich palladium

and platinum clusters. Dalton Trans. 2014, 43, 3114-3120.


20

11. Steinke, T.; Gemel, C.; Winter, M.; Fischer, R. A., The Clusters [Ma(ECp*)b] (M=Pd,

Pt; E=Al, Ga, In): Structures, Fluxionality, and Ligand Exchange Reactions. Chem. Eur. J.

2005, 11, 1636-1646.

12. Buchin, B.; Gemel, C.; Cadenbach, T.; Fernández, I.; Frenking, G.; Fischer, R. A.,

“Naked” Ga+ and In+ as Pure Acceptor Ligands: Structure and Bonding of

[GaPt(GaCp*)4][BArF]. Angew. Chem., Int. Ed. 2006, 45, 5207-5210.

13. Halbherr, M.; Bollermann, T.; Gemel, C.; Fischer, R. A., Selective Oxidative Cleavage

of Cp* from Coordinated GaCp*: Naked Ga+ in [GaNi(GaCp*)4]+ and [(μ2-

Ga)nM3(GaCp*)6]n+ Angew. Chem., Int. Ed. 2010, 49, 1878-1881.

14. Bulychev, B. M., A new stage in the development of transition metal alumohydrides.

Polyhedron 1990, 9, 387-408.

15. Duchateau, R.; Meetsma, A.; Teuben, J. H., Sterically crowded monomeric neutral

bis(benzamidinato) compounds of aluminium, [PhC(NSiMe3)2]2AlX (X = Cl, H); X-ray

crystal structure of [PhC(NSiMe3)2]2AlH. Chem. Commun. 1996, 223-224.

16. Natta, G.; Pino, P.; Mazzanti, G.; Longi, P.; Bernardini, F., The Reaction between

Styrene and Triisobutylaluminum. J. Am. Chem. Soc. 1959, 81, 2561-2563.

17. Spielmann, J.; Buch, F.; Harder, S., Early Main-Group Metal Catalysts for the

Hydrogenation of Alkenes with H2. Angew. Chem., Int. Ed. 2008, 47, 9434-9438.

18. Harder, S., Molecular early main group metal hydrides: synthetic challenge, structures

and applications. Chem. Commun. 2012, 48, 11165-11177.

19. Mandal, S. K.; Roesky, H. W., Group 14 Hydrides with Low Valent Elements for

Activation of Small Molecules. Acc. Chem. Res. 2012, 45, 298-307.

20. Harder, S., Molecular early main group metal hydrides: synthetic challenge, structures

and applications. Chem. Commun. (Cambridge, U. K.) 2012, 48, 11165-11177.


21

21. Spielmann, J.; Buch, F.; Harder, S., Early main-group metal catalysts for the

hydrogenation of alkenes with H2. Angew. Chem., Int. Ed. 2008, 47, 9434-9438.

22. Zidan, R.; Garcia-Diaz, B. L.; Fewox, C. S.; Stowe, A. C.; Gray, J. R.; Harter, A. G.,

Aluminium hydride: a reversible material for hydrogen storage. Chem. Commun. (Cambridge,

U. K.) 2009, 3717-3719.

23. Orimo, S.-i.; Nakamori, Y.; Eliseo, J. R.; Zuettel, A.; Jensen, C. M., Complex Hydrides

for Hydrogen Storage. Chem. Rev. (Washington, DC, U. S.) 2007, 107, 4111-4132.

24. Choi, H.; Hwang, S., Volatile Amidoalane Compounds for Chemical Vapor Deposition

of Aluminum. Chem. Mater. 1998, 10, 2323-2325.

25. Xenidou, T. C.; Prud'homme, N.; Vahlas, C.; Markatos, N. C.; Boudouvis, A. G.,

Reaction and Transport Interplay in Al MOCVD Investigated Through Experiments and

Computational Fluid Dynamic Analysis. J. Electrochem. Soc. 2010, 157, D633-D641.

26. Hanabusa, M.; Ikeda, M., Wavelength dependence in photochemical vapor deposition

of aluminum film using dimethylaluminum hydride. Appl. Organomet. Chem. 1991, 5, 289-93.

27. Baum, T. H.; Larson, C. E.; Jackson, R. L., Laser-induced chemical vapor deposition of

aluminum. Appl. Phys. Lett. 1989, 55, 1264-6.

28. Aldridge, S.; Downs, A. J., Hydrides of the main-group metals. New variations on an

old theme. Chem. Rev. (Washington, D. C.) 2001, 101, 3305-3365.

29. Uhl, W.; Matar, M., Hydroalumination of nitriles and isonitriles. Z. Naturforsch., B:

Chem. Sci. 2004, 59, 1214-1222.

30. Jones, C.; Rose, R. P., Synthesis and characterisation of tetramethylpiperidinyloxide

(TEMPO) complexes of group 13 metal hydrides. New J. Chem. 2007, 31, 1484-1487.

31. Dagorne, S.; Atwood, D. A., Synthesis, Characterization, and Applications of Group 13

Cationic Compounds. Chem. Rev. (Washington, DC, U. S.) 2008, 108, 4037-4071.


22

32. Roesky, H. W., Hydroalumination reactions in organic chemistry. Aldrichimica Acta

2004, 37, 103-108.


23

3.

Oxidation of Ni-ECp* Complexes: Stable Open-Shell NiI Cations

[Ni(ECp*)n(PPh3)4−n]+ (n = 2, 4; E = Al, Ga)

Jiyeon Kim, Markus Halbherr, Christian Gemel, and Roland A. Fischer


24

3 Oxidation of Ni-ECp* Complexes: Stable Open-Shell NiI Cations

[Ni(ECp*)n(PPh3)4−n]+ (n = 2, 4; E = Al, Ga)1

3.1 Abstract

Uncommon NiI cationic complexes were synthesized by treating [Ni(ECp*)2(PPh3)2] (E = Al

or Ga, Cp* = pentamethylcyclopentadienyl) with one equivalent of [FeCp2][BAr4F]. All

compounds have been prepared readily in a high yield. The paramagnetic compounds were

characterized by single crystal X-ray crystallography, Mass spectroscopy, elemental analysis,

magnetic susceptibility and EPR spectroscopy.

3.2 Introduction

During the past two decades the coordination chemistry of low-valent EIR (E = Al, Ga) ligands

to transition metals has been thoroughly investigated. In the case of Cp*, so far every reported

monomeric homoleptic [M(Ecp*)] complex is a saturated species containing 18 valence

electrons (VE). This feature is independent of the used transition metal M. However, for GaR

species containing bulkier R groups, i.e. β-diketiminates (e.g. Ga(ddp) with ddp =

CH(CMeNC6H3(C6H3Pri2-2,6))2) or guanidinates (e.g. Ga(guan) with guan = (C6H3Pri

2-

2,6)NC(NCy2)N(C6H3Pri2-2,6) unsaturated species including [(1,3-cod)Pt(Ga(ddp))2]

4 (cod =

cyclooctadiene) or [Pt(Ga(guan))3] have been reported. The very strong and polar M-E bond

is responsible for the reactivity of these class of mixed-metal complexes. In these compounds

1 The results presented in this chapter have been published in a peer reviewed journal. Reprinted

with permission from Inorg. Chem., 2015, 54 (20), pp 9675–9677. Copyright (2015) American

Chemical Society.


25

the ligand dissociation is prevented by the close vicinity of the nucleophilic M and electrophilic

E. Strong and weakly polar bond such as C-H, Si-H or C-C bonds were activated by compounds

with this interesting electronic settings. To further elucidate this correlation, recent studies

deployed by our group focused on investigating the behavior of [M(ECp*)n] complexes towards

strong one-electron oxidizing agents, for example ferrocenium salts. Suprisingly, neither for

[M(GaCp*)4] (M = Ni, Pt) nor for [Pd3(GaCp*)8] a reaction on the metal-site was observed but

on the organic ligand sphere, leading to the removal of decamethylfulvalene as a dimerization

product of the cp* radical. The reaction products were [Ni(GaCp*)4(Ga)]+ as well as the

triangular clusters [M3(GaCp*)6(Ga)n]n+ (M = Pd, Pt; n = 1, 2), which contained “naked” Ga+

ions as terminal or bridging ligands, respectively. Whithin this chapter, the oxidation of

[Ni(ECp*)n(PPh3)(4−n)] complexes (E = Al, Ga; n = 2, 4) by [FeCp2][OTf] and [FeCp2][BAr4F]

(OTf = trifluoromethanesulfonate; Cp = cyclpentadienyl; BAr4F = B[3,5-(CF3)2C6H3]4) will be

discussed. Interestingly, [Ni(ECp*)n(PPh3)(4−n)]+ cations are formed by oxidation of the

transition-metal center, which reveal the oxidation state NiI. Outstaningly, these products are

the first mixed d-block metal/main-group metal open-shell complexes ever reported and

represent new examples for only a handful known organometallic monomeric open-shell d9

complexes.8

In general the oxidation state 1+ for nickel is uncommon, however, in fact, a few stable

compounds have been reported in the literature. For example the tetraazamacrocycle [Ni(tmc)]+

(tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) is an important model for

enzymatic processes e.g. Acetyl-CoA synthesis. This structure is also related to the methyl

coenzyme M Reductase F430 which generates in metabolic reactions in the Achea methane

from thiomethyl compounds. Other stable NiI complexes include [NiCl(NHC)L] [NHC = 1,3-

bis(2,6-diisopropylphenyl)imidazol-2-ylidene; L = NHC, PPh3], which is used for the catalysis

of cross-coupling and amination reactions.10 A number of low coordinate and neutral NiI


26

complexes were investigated by Laskowski and Hillhouse In the recent literature NiI complexes

which were supported by NHC and Cp ligands have been explored. Furthermore, a small

number of cationic compounds have been discovered, such as the tricoordinated and

tetracordinated complexes [NiI(PPh3)3][BF4]13 and [NiI(PMe3)4][BPh4], respectively.14 For the

latter compound a disproportion into Ni0 and Ni was observed, as it is not stable in solution.

3.3 Result and Discussion

The oxidation the Ni(0) centers to Ni(1) is achieved by the addition of one equivalent of

[FeCp2][BAr4F] in fluorobenzene at room temperature to the complexes [Ni(ECp*)2(L)2] (L =

AlCp*, PPh3; E = Al, Ga). The E(I) ligands and the Cp* remain unchanged during this reaction.

Isolation of the complexes [NiI(AlCp*)4][Cp*Al(OTf)3] (1), [NiI(AlCp*)2(PPh3)2]-[BAr4F] (2)

and [NiI(GaCp*)2(PPh3)2][BAr4F] (3) was possible. Noticeably 1 is thermally highly unstable

and decomposes during workup, hence only few crystals were isolated and were used for

characterization. On the other hand, compounds 2 and 3 were stable at inert conditions at room

temperature either in the solid state as well as in solution.

A quite suprising result is the finding that the trasition metal center is oxidized instead of the

ECp* ligand. In particular, because for the analogous compound [Ni(GaCp*)4] the oxidation

Scheme 3.3.1 Synthesis of NiI Compounds 1-3


27

by [FeCp2][BAr4F] resulted in the formation of [NiGa(GaCp*)4]

+ containing Ga+ moieties.

Additionally, in the case of analogous palladium and platinum complexes a similar oxidation

accompanied by the formation of decamethylfulvalene.

The compounds 1-3 are crystallized from a mixture of fluorobenzene and hexane. In Figure

3.3.1 depiction of the molecular structures of all three compounds is displayed and in Table

3.6.1 all important structural paramters are summarized. An overview of the important

interatomic distances is given in Table 3.6.2. No complete single crystal diffraction datasets of

compound 1 could be obtained, because of the high instability of this material. During the

experiment the compound slowly decomposed. However, an overall completeness of 80 % with

a final data to parameter ratio of 9:1 could be achieved and also a sufficiently good R value

leads to high confidence in the interpretation of the diffraction data. More or less strong

distortions of the tetrahedral coordination environment of the Ni center was observed in all

three compounds. Particularly obvious was this finding for the homoleptic complex 1, where

the Al-Ni-Al angles amount to 103.23(15) ° and 132.00(17) °. In the parent, neutral [Ni(AlCp*)4]

species the ideal tetrahedral angles of 109.5° are present. The Jahn-Teller distortion is held

accountable for this flattening of the structure with the prototypical [CuCl4]2- as an example.

For the similar homoleptic cation [Ni(PMe3)4]+ similar distortions were observed (104.6(1)° to

119.9(1)°). Even larger distortion have been found in the phosphine substituted complex 2 and

3 with angles between 98.07(4)° and 131.24(4)°) and 3 (L-Ni-L angles between 98.75(2)° and

134.35(3)°, respectively. This is caused most probably by the steric repulsion of the very bulky

PPh3 ligands. Notably, no indication for hydride species were found using spectroscopic

methods (NMR). Additionally, the compounds are all paramagnetic, which was confirmed by

EPR spectroscopy.


28

The Ni-E bond distances are only slightly affected by the oxidation. The mean Ni-Al distance

amounts to 2.17 Å in [Ni(AlCp*)4]+ and is the same in the parent neutral compound

[Ni(AlCp*)4]. In the phosphine substituted species a slight increase is observed in the Ni-Al

bond upon oxidation, from 2.21 Å to 2-27 Å and from 2.25 Å to 2.32 Å in compounds 2 and 3,

respectively. Moreover, a decrease of the E-Cp*centroid distance was found, most likely because

of the increase of the E-Cp* bonds polarity. This is induced by the over-all positive charge of

the complex.

Figure 3.3.1 Molecular structure (POV-Ray Plot) of the cationic parts of the salts 1-3, namely

[Ni(AlCp*)4]+ (1), [Ni(AlCp*)2(PPh3)2]

+ (2) and [Ni(GaCp*)2(PPh3)2]+ (3) in the solid state as

determined by single crystal X-ray diffraction; displacement ellipsoids are shown at the 50%

probability level, hydrogen atoms are omitted for clarity. Selected interatomic distances and angles are

summarized in Table 3.6.2.


29

Broad signals in the 1H-NMR spectra of compounds 2 and 3 indicate their paramagnetic nature.

Nonetheless, in the 31P-NMR unusually sharp signals were observed. Via Evans NMR method

at room temperature the magnetic susceptibility (eff) of these complexes were determined.

Values for eff of 1.09 BM and 1.15 BM were calculated in fluorobenzene (BM = Bohr

Magnetron). These values are slightly lower than the theoretically calculated values for NiI in

tetrahedral geometry (1.73 BM). These two compounds showed also EPR activity, with average

g-factors of 2.11 and 2.15 for 2 and 3 respectively. (Figure 3.6.3) These findings are in

accordance with other NiI complexes. The recorded spectra are highly complex and thus the

hyperfine couplings of the EPR signals could not be simulated. The cation peaks of these two

complexes were also revealed using liquid injection field desorption ionization mass

spectrometry (LIFDI-MS), with the cation peaks at m/z [a.u] of 906 and 993 for compounds 2

and 3, respectively.

3.4 Conclusion

Using the more electrophilic metal ligator Al, both the homoleptic [Ni(AlCp*)4] and the

phosphine containing analogue [Ni(AlCp*)2(PPh3)2] yield cationic 17 VE complexes (1 and 2).

For the metal Ligator Ga, only the heteroleptic complex [Ni(GaCp*)2(PPh3)2] is reacting in the

same fashion, yielding 3. The homoleptic [Ni(GaCp*)4] complexe yields after oxidation the

cation [Ni(GaCp*)4(Ga)]+ featuring naked Ga. This is because the cleavage of a C5Me5 radical

occurs easier on the less polar E-Cp* bond, showcased by the homoleptic GaCp* substituted

Nickel complex. Furthermore, the substitution of ECp* by PPh3 forms more electron deficient

metal centers increasing the polarity of the E-Cp* bond.


30

3.5 References

(1) (a) Asay, M.; Jones, C.; Driess, M. Chem. Rev. 2011, 111, 354-396; (b) Molon, M.;

Bollermann, T.; Gemel, C.; Schaumann, J.; Fischer, R. A. Dalton Trans. 2011, 40, 10769-10774;

(c) Steinke, T.; Cokoja, M.; Gemel, C.; Kempter, A.; Krapp, A.; Frenking, G.; Zenneck, U.;

Fischer, R. A. Angew. Chem., Int. Ed. 2005, 44, 2943-2946; (d) Steinke, T.; Gemel, C.; Cokoja,

M.; Winter, M.; Fischer, R. A. Angew. Chem., Int. Ed. 2004, 43, 2299-2302; (e) Steinke, T.;

Gemel, C.; Winter, M.; Fischer, R. A. Chem. Eur. J. 2005, 11, 1636-1646; (f) Bollermann, T.;

Cadenbach, T.; Gemel, C.; von Hopffgarten, M.; Frenking, G.; Fischer, R. A. Chem. Eur. J.

2010, 16, 13372-13384.

(2) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000, 1991-1992.

(3) Jones, C.; Junk, P. C.; Platts, J. A.; Stasch, A. J. Am. Chem. Soc. 2006, 128, 2206-2207.

(4) Kempter, A.; Gemel, C.; Fischer, R. A. Chem. Eur. J. 2007, 13, 2990-3000.

(5) Green, S. P.; Jones, C.; Stasch, A. Inorg. Chem. 2007, 46, 11-13.

(6) Cadenbach, T.; Gemel, C.; Schmid, R.; Block, S.; Fischer, R. A. Dalton Trans. 2004, 3171-

3172.

(7) Halbherr, M.; Bollermann, T.; Gemel, C.; Fischer, R. A. Angew. Chem., Int. Ed. 2010, 49,

1878-1881.

(8) Margulieux, G. W.; Weidemann, N.; Lacy, D. C.; Moore, C. E.; Rheingold, A. L.; Figueroa,

J. S. J. Am. Chem. Soc. 2010, 132, 5033-5035.

(9) (a) Ram, M. S.; Riordan, C. G.; Ostrander, R.; Rheingold, A. L. Inorg. Chem. 1995, 34,

5884-5892; (b) Ram, M. S.; Yap, G. P. A.; Liable-Sands, L.; Rheingold, A. L.; Marchaj, A.;


31

Norton, J. R. J. Am. Chem. Soc. 1997, 119, 1648-1655; (c) Lafrance, M.; Gorelsky, S. I.; Fagnou,

K. J. Am. Chem. Soc. 2007, 129, 14570-14571; (d) Telser, J. J. Braz. Chem. Soc. 2010, 21,

1139-1157.

(10) Nagao, S.; Matsumoto, T.; Koga, Y.; Matsubara, K. Chem. Lett. 2011, 40, 1036-1038.

(11) (a) Laskowski, C. A.; Hillhouse, G. L. J. Am. Chem. Soc. 2008, 130, 13846-13847; (b)

Anderson, J. S.; Iluc, V. M.; Hillhouse, G. L. Inorg. Chem. 2010, 49, 10203-10207; (c) Iluc, V.

M.; Hillhouse, G. L. J. Am. Chem. Soc. 2010, 132, 15148-15150; (d) Lipschutz, M. I.; Yang,

X.; Chatterjee, R.; Tilley, T. D. J. Am. Chem. Soc. 2013, 135, 15298-15301.

(12) (a) Wu, J.; Nova, A.; Balcells, D.; Brudvig, G. W.; Dai, W.; Guard, L. M.; Hazari, N.; Lin,

P.-H.; Pokhrel, R.; Takase, M. K. Chem. Eur. J. 2014, 20, 5327-5337; (b) Pelties, S.; Herrmann,

D.; de Bruin, B.; Hartl, F.; Wolf, R. Chem. Commun. 2014, 50, 7014-7016.

(13) Saraev, V. V.; Kraikivskii, P. B.; Svoboda, I.; Kuzakov, A. S.; Jordan, R. F. J. Phys. Chem.

A 2008, 112, 12449-12455.

(14) Gleizes, A.; Dartiguenave, M.; Dartiguenave, Y.; Galy, J.; Klein, H. F. J. Am. Chem. Soc.

1977, 99, 5187-5189.

(15) (a) Helmholz, L.; Kruh, R. F. J. Am. Chem. Soc. 1952, 74, 1176-1181; (b) Willett, R. D.;

Larsen, M. L. Inorg. Chim. Acta 1971, 5, 175-179.

(16) (a) Hüttner, W.; Flygare, W. H. J. Chem. Phys. 1969, 50, 2863-2868; (b) de Luca, G.;

Russo, N.; Sicilia, E.; Toscano, M. J. Chem. Phys. 1996, 105, 3206-3210; (c) Bloor, J. E.;

Maksić, Z. B. Mol. Phys. 1973, 26, 397-408; (d) Hoppe, J. I. J. Chem. Educ. 1972, 49, 505; (e)

Bain, G. A.; Berry, J. F. J. Chem. Educ. 2008, 85, 532; (f) Flygare, W. H.; Benson, R. C. Mol.

Phys. 1971, 20, 225-250; (g) Piguet, C. J. Chem. Educ. 1997, 74, 815; (h) Sur, S. K. J. Magn.

Reson. 1989, 82, 169-173.


32

(17) (a) Kotani, M. Progr. Theor. Exp. Phys. Supp. 1961, 17, 4-13; (b) Petuker, A.; Merten, C.;

Apfel, U.-P. Eur. J. Inorg. Chem. 2015, 2015, 2139-2144.

(18) Eckert, N. A.; Dinescu, A.; Cundari, T. R.; Holland, P. L. Inorg. Chem. 2005, 44, 7702-

7704


33

3.6 Experimental Section

3.6.1 General Comments

Material and Methods. All manipulations were carried out in an atmosphere of purified argon

using standard Schlenk and glove-box techniques. n-Hexane was dried using an MBraun

Solvent Purification System and fluorobenzene and d6-benzene were dried by passing through

a column of dried activated neutral Al2O3. The final H2O content in all solvents was checked

by Karl Fischer titration and did not exceed 5 ppm. [AlCp*]1, [GaCp*]2, [Ni(AlCp*)4]3,

[Ni(AlCp*)2(PPh3)2]4, [Ni(GaCp*)2(PPh3)2]

4, [FeCp2][BAr4F]5 and [FeCp2][OTf]6 were

prepared as previously described in the literature. Elemental analyses were performed by the

Microanalytical Laboratory (Rubiospek) of the Ruhr-University Bochum. The LIFDI mass

spectra were measured with a Jeol AccuTOF GCv spectrometer with a Linden-CMS.de LIFDI

source. NMR spectra of paramagnetic substances were recorded on a Bruker Avance DPX-250

spectrometer in fluorobenzene/benzene (10:1 v/v ratio) solution at 298 K. Effective magnetic

moment calculated by Evan’s method was conducted in fluorobenzene and dichloromethane

with chemical shifts given relative to TMS and were referenced to the residual solvent. The

chemical shifts are described in parts per million (ppm), downfield shifted from TMS and are

consecutively reported as position (δ H, δ P, δ B), relative integral, multiplicity (s = singlet, m

= multiplet), coupling constant (J in Hz) and assignment. EPR spectra were measured with an

X-band spectrometer in fluorobezene at 16 K (Bruker ELEXSYS500 X-band spectrometer).

FT-IR spectra were measured on a Bruker Alpha FT-IR spectrometer. The molecular structures

were measured on an Agilent Technologies SuperNova diffractometer with an Atlas CCD


34

detector, using CuK radiation (λ = 1.541 84 Å) from multilayer X-ray optics. The crystals were

coated with a perflusotopolyether, picked up with a cryo loop, and immediately mounted in the

nitrogen cold gas stream of the diffractometer. The data were processes with CrysAlisPro.7 The

crystal structure was solved by direct methods using SHELXS-97 and refined with SHELXL-

2013.19 Two of the CF3 groups of the BAr4F anion show rotational disorder.8

3.6.2 Synthetic Procedures

[Ni(AlCp*)4][Cp*Al(OTf)3] (1) [Ni(AlCp*)4] (100 mg, 0.141 mmol) was dissolved in

fluorobenzene (5 ml) and [FeCp2][OTf] (47 mg, 0.141 mmol) was suspended in fluorobenzene

(5 ml) in a different schlenk tube and both cooled with an iso-propanol/dry-ice bath to -35°C.

The latter suspension of [FeCp2][OTf] was transferred slowly via cannula to [Ni(AlCp*)4]

giving a deep red solution. Storage at -30°C for 3 months gave few crystals suitable for single

crystal x-ray diffraction. Because of very low stability of the compound 1, further

characterization could not be done.

[Ni(AlCp*)2(PPh3)2][BAr4F] (2) [Ni(AlCp*)2(PPh3)2] (100 mg, 0.110 mmol) and

[FeCp2][BAr4F] (116 mg, 0.110 mmol) were dissolved in fluorobenzene (5 ml) and stirred for

1 h during which the color changed from deep red to dark green. Crystals suitable for single

crystal x-ray diffraction were obtained by layering the fluorobenzene solution with n-hexane.

Anal. Calcd. (found) for C88H72BF24Al2NiP2: C 59.68% (59.04%); H 4.1% (4.11%). LIFDI-MS:

m/z = 906.4 [M] +, for the cation [Ni(AlCp*)2(PPh3)2]+. 1H-NMR (C6H5F/10% C6D6): δ 10.10

ppm, 1.10 ppm. 31P-NMR : 53.16 ppm.


35

[Ni(GaCp*)2(PPh3)2][BAr4F] (3) [Ni(GaCp*)2(PPh3)2] (100 mg, 0.101 mmol) and

[FeCp2][BAr4F] (106 mg, 0.101 mmol) were dissolved in fluorobenzene (5 ml) and stirred for

1 h during which the color changed from deep red to light red. Crystals suitable for single crystal

x-ray diffraction were obtained by layering the fluorebenzene solution with n-hexane. Anal.

Calcd. (found) for C88H72BF24Ga2NiP2: C 56.98 % (56.53 %); H 3.92 % (4.01 %). LIFDI-MS:

m/z = 993.0 [M] + for the cation [Ni(GaCp*)2(PPh3)2]+. 1H-NMR (C6H5F/10% C6D6): δ 11.32

ppm, 3.77 ppm. 31P-NMR : 48.84 ppm.

Comment to the x-ray diffraction experiment of 1:

The high chemical instability and sensitivity of 1 also at low temperatures leads to slow

decomposition of the single crystal during the x-ray diffraction experiment and no complete

dataset was available. However, the overall completeness of 80%, a final data:parameter ratio

of 9:1 and sufficiently good R values (R1=0.0485) allow a consistent interpretation of the

data, and therefore a structural discussion of this compound has been included in the

manuscript.


36

3.6.3 Spectroscopic and crystallographic data

Figure 3.6.1 31P, 1H and 11B NMR spectra of compound 2 [Ni(AlCp*)2(PPh3)2][BAr4F] in 10 %

d6-benzene in fluorobenzene.


37


38


39


40

Figure 3.6.2 NMR spectra of compound 3 [Ni(GaCp*)2(PPh3)2][BAr4F] in 10 % d6-benzene in

fluorobenzene.


41


42


43

Figure 3.6.3 EPR spectra of compound 2 [Ni(AlCp*)2(PPh3)2][BAr4F] (left) and 3

[Ni(GaCp*)2(PPh3)2][BAr4F] (right). The average g-factors for 2 (g = 2.11) and 3 (g = 2.15)

were obtained. The measurements were reproduced at 6 K on a different instrument (Varian

E112 EPR- Spectrometer (X-Band)) with identical results. The interpretation of the hyperfine

couplings of the highly complicated EPR signals is not possible.

1000 2000 3000 4000 5000 6000

B (G)

1000 2000 3000 4000 5000

B (G)


44

Figure 3.6.4 UV-Vis (black) and Photoluminescence (PL, blue) spectra of compound 2 (left)

and 3 (right).The UV-Vis and PL were measured in fluorobenzene solution. The spectra of UV-

Vis/PL of compound 2 and 3 show absorbance band and emission peak at abs = 350 nm, em =

404, 428 nm and abs = 355, 444 nm, em = 404, 428 nm.


45

Crystallographic Data

Table 3.6.1 Important crystallographic data of compounds 1, 2 and 3

1 2 3

Empirical formula C59H75Al5F10NiO9S3 C88H72Al2BF24NiP2 C88H72BF24Ga2NiP2

Formula weight 1407.98 1770.88 1856.36

Temperature (K) 108.15 104.15 110.15

Crystal system monoclinic monoclinic monoclinic

Space group Cc P21/n P21/n

a/Å 16.7480(8) 20.4713(5) 20.5202(3)

b/Å 15.5917(9) 20.1109(4) 20.1408(2)

c/Å 26.5642(15) 20.5530(5) 20.5787(3)

α/° 90 90 90

β/° 95.151(5) 101.560(2) 101.965(1)

γ/° 90 90 90

Volume/Å3 6908.7(6) 8290.0(3) 8320.26(19)

Z 4 4 4

ρcalcg/cm3 1.354 1.419 1.482

μ/mm-1 0.512 0.393 1.004

F(000) 2928 3620 3764

Crystal size/mm3 0.15 × 0.12 × 0.09 0.14 × 0.12 × 0.10 0.17 × 0.14 × 0.09

Radiation MoKα (λ = 0.71073) MoKα (λ = 0.71073) MoKα (λ = 0.71073)

2Θ range for data collection/° 5.666 to 48.498 5.72 to 58 5.72 to 55.12

Index ranges -17 ≤ h ≤ 17 -26 ≤ h ≤ 27 -26 ≤ h ≤ 26

-11 ≤ k ≤ 17 -26 ≤ k ≤ 26 -26 ≤ k ≤ 26

-28 ≤ l ≤ 27 -26 ≤ l ≤ 27 -25 ≤ l ≤ 26

Reflections collected 11368 157220 152416

Data/restraints/parameters 6835/56/784 20038/0/1063 19082/0/1073

Goodness-of-fit on F2 0.789 1.025 1.02

Final R indexes [I>=2σ (I)] R1 = 0.0485 R1 = 0.0704 R1 = 0.0460

wR2 = 0.0668 wR2 = 0.1517 wR2 = 0.1016

Final R indexes [all data] R1 = 0.1000 R1 = 0.1343 R1 = 0.0736

wR2 = 0.0746 wR2 = 0.1792 wR2 = 0.1136

Largest diff. peak/hole / e Å-3 0.48/-0.30 1.39/-0.88 1.29/-0.85


46

Table 3.6.2 Selected interatomic distance [Å] and angle [°]

1 2 3

Ni-Al1 2.181(4) Ni-Al1 2.260(1) Ni-Ga1 2.310(1)

Ni-Al2 2.147(4) Ni-Al2 2.287(1) Ni-Ga2 2.329(1)

Ni-Al3 2.195(3) Ni-P1 2.178(1) Ni-P1 2.213(1)

Ni-Al4 2.142(4) Ni-P2 2.189(1) Ni-P2 2.204(1)

Al1-Cp*centroid 1.876 Al1-Cp*centroid 1.857 Ga1-Cp*centroid 1.933

Al2-Cp*centroid 1.854 Al2-Cp*centroid 1.873 Ga2-Cp*centroid 1.942

Al3-Cp*centroid 1.851

Al4-Cp*centroid 1.844

Al1-Ni-Al2 103.26(14) Al1-Ni-Al2 108.54(5) Ga1-Ni-Ga2 117.30(2)

Al1-Ni-Al3 112.83(16) P1-Ni-P2 131.24(4) P1-Ni-P2 134.35(3)

Al1-Ni-Al4 100.85(15) P1-Ni-Al1 98.07(4) P1-Ni-Ga1 100.25(2)




Ni-Al1-Cp*centroid 173.13(166) Ni-Al1-Cp*centroid 174.12(7) Ni-Ga1-Cp*centroid 168.74 (2)

Ni-Al2-Cp*centroid 167.44(17) Ni-Al2-Cp*centroid 172.91(6) Ni-Ga2-Cp*centroid 175.45 (2)

Ni-Al3-Cp*centroid 177.88(14)

Ni-Al4-Cp*centroid 170.81(16)


47

4 References

(1) S. Schulz, H. W. Roesky, H. J. Koch, G. M. Sheldrick, D. Stalke and A. Kuhn, Angew.

Chem. Int. Ed., 1993, 32, 1729–1731.

(2) P. Jutzi, B. Neumann, G. Reumann and H.-G. Stammler, Organometallics, 1998, 17, 1305–

1314.

(3) Steinke, T.; Gemel, C.; Cokoja, M.; Winter, M.; Fischer, R. A Angew. Chem. Int. Ed, 2004,

43, 2299–2302.

(4) M. Molon, T. Bollermann, C. Gemel, J. Schaumann, R. A. Fischer, Dalton Trans, 2011.

(5) J. Le Bras, H. Jiao, W. E. Meyer, F. Hampel and J. A. Gladysz, J. Organomet. Chem., 2000,

616, 54–66.

(6) Z.-W. Li, A. Yeh and H. Taube, Inorg. Chem., 1994, 33, 2874–2881.

(7) CrysAlisPro Software System, version 1.171.36.20; AgilentTechnologies UK Ltd.: Oxford,

U.K., 2012.

(8) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.


48

4. Organoaluminum Palladium Complex via Reductive

Elimination

Jiyeon Kim, Hung Banh, Mathies Evers, Christian Gemel, Roland A. Fischer


49

4. Organoaluminum Palladium Complex via Reductive

Elimination

4.1 Abstract

The reaction of AlIII hydride species and palladium phosphine complexes is described in this

chapter. The reaction product [(PCy3)Pd-2-AlCp*]2 was obtained via reductive elimination of

hydrogen and characterized by NMR spectroscopy, LIFDI-MS, single crystal X-ray diffraction.

4.2 Introduction

There has been a significant amount of efforts from fundamental organometallic chemists to

access heterometallic complexes containing direct metal-metal bonds. Although, several

classical methods are known, such as oxidative addition etc., metal-metal coupling still remains

a challenge. The coordination chemistry of low valent EIR species towards transition metals

opened new doors in intermetallic chemistry. Since EIR is an isolobal analog of CO and

phosphine, many group 6-12 transition metal complexes containing EIR with the fomular

[M(EIR)n] have been investigated.


50

In 2012, Ganesamoorthy et al. reported a new synthetic pathway for synthesizing [AlICp*]4

(Cp* = pentamethylcyclopentadienyl) via reductive elimination.1 This procedure suggested a

route with a mechanism distinct from the literature known procedure (Schnöckel)2. Thermally

induced reaction of AlIIICp*2H leads to the formation of [AlCp*]4 which includes the formation

of a direct Al-Al bond via reductive elimination of Cp*H. This work was an inspiration of

preparing intermetallic complexes including bonds between transition metals and group 13

metals via intramolecular reductive elimination. Even though, reductive elimination in

transition metal-complexes is commonly observed particularly in small molecule activations

(C-H or C-C coupling), reports on intramolecular reductive elimination resulting in direct

metal-metal bonds remain scarce. Herein, we report the formation of Pd-Al bonds via reductive

elimination of H2.


The stoichiometric reaction of Pd(PCy3)2 (Cy = cyclohexyl) and AlCp*H2 in benzene

reductively eliminates H2 thermally at 70 °C. (Scheme 4.1) Additionally, the loss of one

equivalent of free PCy3 affords [(PCy3)Pd-2-AlCp*]2 (4). Reaction completeness was

monitored by in-situ 1H-NMR spectroscopy. A strong gas evolution was already observed as

soon as benzene was added into a J-Young NMR tube before sealing. Although, in-situ 1H

NMR measurements show a weak but clear evidence of H2 evolution at 4.46 ppm from the

H2 cleavage in AlCp*H2. (Figure 4.4) Compound 4 decomposes in air and is moisture sensitive

and readily dissolve in non-polar solvents such as hexane or toluene. The chemical shift of

bridging AlCp* from compound 4 was observed at 2.14 ppm whereas AlCp* and AlCp*H2

protons appear at 1.89 and 1.91 ppm. Protons in the phosphine ligand are displayed as broad


51

peaks at 1.22 and 1.72 ppm, whereas the protons of free phosphine appear in the area of 1.26

– 2.24. The 31P NMR spectrum of compound 4 shows a resonance at 57.09 ppm with trace

amounts of free PCy3 at 9.97 ppm. the reactant Pd(PCy3)2 has the phosphine resonance peak

at 39.18 ppm and cannot be identified in the final product. Compound 4 could not be

completely isolated from free PCy3 by recrystallization due to the indistinct solubility

differences. Liquid injection field desorption ionization mass spectrometry (LIFDI-MS) of 4

clearly identifies molecular ion peak at m/z 1098.17. This observation indicates there is no

hydride takes place in the molecule particularly at the two palladium atoms. Moreover, the

transition metal hydrides exhibit the IR vibration near 2000 cm-1 where no peak has been

observed in this area. (Figure 4.7)

Scheme 4.1 Reaction of Pd(PCy3)2 with AlCp*H2

Crystals suitable for single crystal X-ray diffraction are obtained in pentane at -30 °C. Figure

4 shows a depiction of the molecular structure of 4. Crystallographic data and refinement details

are shown in Table 4.1 whereas important bond distance and angles are shown in Table 4.2.

The solvate free compound 4 crystallizes in the monoclinic space group C2/c with two

fragments in the asymmetric unit. The molecular structure of the type [Pd2Al2P2] has two

bridging AlCp* and two cis-terminal phosphine ligands with a geometry described best as two

edge-sharing trigonal planar units. (Figure 4.2) The two aluminum atoms are shared within

both units. The two bridging AlCp*s are bent to lopsided with an angle of Pd−Pd axis and two

aluminum atoms found 130.7°. Interestingly, the two terminal phosphines are bent to opposite


52

direction of AlCp* ligands resulting in a P−Pd−Pd angle of 152.7 °. (Figure 4.1) These effects

explain the biased structure of bridging AlCp* of compound 4. In comparison to previous

observations by Fischer et al. where the compounds [Pd2(GaCp*)3(PMe3)2]3-4 [Mariusz Dalton

2014] and [Pd2(GaCp*)3(PPh3)2] [Steinke 2005 chemeurj] with a similar core building unit but

with three bridging ligands of the type [Pd2Ga3P2] was reported, quite different results regarding

the bonding situation were found. The angle of P-Pd-Pd in those structures, the tree atoms are

in linear positions in contrast to compound 4. Also, the steric bulk cyclohexyl groups in

phosphine are inclined to the opened site of Pd−Pd bond which consequently stabilize the

structure (Figure 2). The Pd1-Pd2 bond length of 2.592 Å in compound 4 is slightly shortened

than as found for the Pd0-Pd0 complexes [Pd2(AlCp*)5]4 [Steinke 2005 chemeurj] and

[Pd2(GaCp*)3(PMe3)2]3 [Mariusz Dalton 2014] (2.633(1); and 2.623(1)). The bridging Pd−Al

bond length of 4 (a 2.424 Å) is in the same range as found in [Pd2AlCp*5] (a 2.448 Å). [Steinke

chemeurj 2005]

Figure 4.1 Povray plot of the molecular structure of 1 in the solid state as determined by single

crystal X-ray diffraction (the asymmetric unit contains two molecules; thermal ellipsoids are

shown 50 % probability; hydrogen atoms are omitted for clarity). Selected atomic distances (Å)

as well as angles (°): Pd1−Pd2: 2.5914(6), Al1−Pd1: 2.4284(15), Pd1−Al2: 2.4102(14),

Pd2−Al2: 2.4201(15), Pd2−Al1: 2.4377(15), Pd1−P1: 2.2807 (13), Pd2−P2: 2.2936(13),


53

Al−Cp*: a1.951, Pd1−Al1−Pd2: 100.25(5), Pd1−Al2−Pd2: 99.71(5), Cp* values are calculated

from the centroid of the Cp* moiety.

Figure 4.2 Illustration of coordination geometry of compound 1 (M2Al2P2) and the

comparison of molecular type M2Ga3P2.

4.4 Conclusion

Within this chapter a facile route to a dinuclear Pd core structure with heteroleptic ligand

coordination sphere was presented. Reductive elimination was used as a tool to prepare this

new structure. Regarding the state of the art, this is the first described synthesis of a transition

metal−group 13 complex via this mechanistic route. It is highly expected that this synthetic

approach can help to extend the possibilities in constructing compounds containing metal-metal


54

bonds and will help open up new doors in the field of organomettalic chemistry. Furthermore,

we showed a new Pd2Al2P2 core with aluminum ligands which have been directed by the steric

bulk of the R groups on the P ligands. The found geometry is very uncommon and the

assymetric palladium dimer with relatively unshielded metal site might be of interest as a

building unit to access intermetallic clusters.


55



All manipulations were carried out in an atmosphere of purified argon using standard Schlenk

and glove-box techniques. n-Hexane and n-pentane were dried using an MBraun Solvent

Purification System. Benzene was dried by passing through a column of dried activated neutral

Al2O3. d6-Benzene was degassed and stored under the molecular sieves (4 Å). All the

instruments for characterization were identically used described in section 3.6. [AlCp*H2] and

[Pd(PCy3)2] were prepared as previously described in the literature. [Ganesh + a]

4.5.2 Synthetic procedure

[(Pd(AlCp*)(PCy3))2] Pd(PCy3)2 (200 mg, 0.300 mmol) and AlCp*H2 (50 mg, 0.305 mmol)

were dissolved in benzene (5 ml), immediate colour change to dark red and gas evolution were

observed. The reaction mixture was stirred for 1 h at 80 °C. All the volatiles were removed

under vacuum and the residue was extracted with cold (- 60 °C) pentane. Dark-red crystals

suitable for single crystal x-ray diffraction were obtained at -30 °C in the concentrated pentane

solution. 1H-NMR (C6D6): 2.14 ppm (Cp*Al), 1.77-1.72 ppm (Cy3P). 31P-NMR (C6D6):

57.09 ppm (P-Pd). LIFDI-MS: m/z = 1098.2 [M] +, for the cation [(Pd(AlCp*)(PCy3))2]+.


56

4.5.3 Spectroscopic, Spectrometric, Crystallographic Data

Figure 4.3 LIFDI-MS data of 1 in toluene solution


57

Figure 4.4 1H-NMR from the NMR reaction of Pd(PCy3)3 and AlCp*H2 in 1:1 ratio in d6-

benzene. Hydrogen (H2) is observed at 4.46 ppm.


58

Figure 4.5 1H-NMR of compound 4 in d6-benzene. 2.14 ppm (Cp*Al); 1.77-1.72 ppm

(Cy3P).


59

Figure 4.6 31P-NMR of compound 4 in d6-benzene. 57.09 ppm, (P-Pd); 9.97 ppm, free

phosphine.


60

Figure 4.7 FT-IR spectrum of compound 4.


61

Table 4.1 Crystallographic data and refinement details of compound 4.

Table S1 Selected Bond Length (Å) and Angles (°) for compound 4.

Pd(1)−Pd(2) 2.5914(6) Pd(1)−Al(1)−Pd(2) 100.25(5)

Pd(1)−Al(1) 2.4284(15) Pd(1)−Al(2)−Pd(2) 99.71(5)

Pd(1)−Al(2) 2.4102(14) P(1)−Pd(1)−Pd(2) 153.70(4)

Pd(2)−Al(2) 2.4201(15) P(1)−Pd(2)−Pd(1) 151.74(4)

Pd(2)−Al(1) 2.4377(15) Al(1)−Pdaxis−Al(2) 130.7

Pd(1)−P(1) 2.2807 (13)

Pd(2)−P(2) 2.2936(13)

Al−Cp*centroid a1.951

a means value

4

Chemical formula C56H96Al2P2Pd2

Formula weight 1098.02

Crystal system Monoclinic

Space group C2/c

a (Å) 71.238(5)

b (Å) 10.2931(3)

c (Å) 45.665(3)

(°) 136.980(12)

Volume (Å3) 22845(4)

Z 16

Dcalc (g × cm-3) 1.277

/mm-1 6.142

F(000) 9280.0

2θ range for data collection (°) 7.276 to 139.998

Reflections collected/unique 42875/20848 [Rint = 0.0564]

Data/restraints/parameters 20848/0/1137

goodness-of-fit on F2 1.006

Final R indices [I > 2(I)] R1 = 0.0469, wR2 = 0.1028

R indices (all data) R1 = 0.0717, wR2 = 0.1503


62

5. References

1. Ganesamoorthy, C.; Loerke, S.; Gemel, C.; Jerabek, P.; Winter, M.; Frenking, G.;

Fischer, R. A., Reductive elimination: a pathway to low-valent aluminium species. Chem.

Commun. 2013, 49, 2858-2860.

2. Dohmeier, C.; Robl, C.; Tacke, M.; Schnöckel, H., The Tetrameric Aluminum(I)

Compound [{Al(η5-C5Me5)}4]. Angew. Chem., Int. Ed. 1991, 30, 564-565.

3. Molon, M.; Gemel, C.; Fischer, R. A., Organogallium- and organozinc-rich palladium

and platinum clusters. Dalton Trans. 2014, 43, 3114-3120.

4. Steinke, T.; Gemel, C.; Winter, M.; Fischer, R. A., The Clusters [Ma(ECp*)b] (M=Pd,

Pt; E=Al, Ga, In): Structures, Fluxionality, and Ligand Exchange Reactions. Chem. Eur. J.

2005, 11, 1636-1646.

PART 2 Precursor Synthesis and Atomic Layer Deposition of Cobalt Oxide

63

PART 2 Precursor Synthesis and Atomic Layer Deposition

of Cobalt Oxide


64

List of Abbreviation

AFM Atomic Force Microscopy

ALD Atomic Layer Deposition

AMD Amidinate

CDI Carbodiimide

Cp Cyclopentadiene

CVD Chemical Vapor Deposition

Cy Cyclohexyl

DTA Differential Thermal Analysis

DSC Differential Scanning Calorimetry

EA Elemental Analysis (CHN)

EDX Energy Dispersive X-ray

EI-MS Electron Impact Mass Spectrometry

Et2O Diethylether

tBu2DAD 1,4-di-tert-butyl-1,3-diazadiene

GI Grazing incidence

GPC Growth per cycle

Guan Guanidinate

Hacac Acetylacetone

HTXRD High Temperature X-ray Diffraction

IR Infra-Red

Me Methyl


65

MOCVD Metalorganic Chemical Vapor Deposition

NMR Nuclear Magnetic Resonance

iPr Isopropyl

PEALD Plasma Enhanced ALD

PVD Physical Vapor Depsoition

RBS Rutherford Backscattering Spectrometry

Rms Root mean square

RT Room Temperature

SEM Scanning Electron Microscopy

tBu tert-butyl

TEM Transmission Electron Microscopy

TGA Thermogravimetric Analysis

Thd 2,2,6,6,-tetramethyl-3,5-heptadione, C11H20O2

THF Tetrahydrofuran

ToF-ERDA Time of Flight Elastic Recoil Detection Analysis

UV Ultraviolet

XPS X-ray Photoelectron Spectroscopy

XRD X-ray Diffraction


66

5. General Introduction


67

5 General Introduction

5.1 General Introduction

Already many examples for thin films possessing functional properties exist in nature, for

instance the brilliant colors of the feathers of a peacock or the wings of butterflies caused by

the interference of light with extremely thin films covering these. Another example for thin

films in daily life are simple household mirrors. Mirrors are nowadays produced by covering a

suitable substrate with a reflective coating. The first attempts on making very crude mirrors in

this fashion were already reported 2000 years ago in Pliny the Elders book on Natural History.

In Sidon, which is located in nowadays Lebanon, circular cuts of brown glass were coated with

molten lead. Since these early reports on the preparation of functional films a lot happened and

many methods have been developed to coat substrate materials in order to improve their

properties for certain useful applications and alter their mechanic, optical, chemical or

electronic functions.

Rusting of steel and iron parts was a big issue in former times, which reduced the stability and

longevity of tools and parts in i.e. machinery and buildings drastically. By applying a thin film

of zinc to the used parts the iron was protected from outer influences and the reaction to iron

oxide (rust) is inhibited. Even in the case of scratching or partly destruction of the zinc layer,

still a protective effect is occurring, as the zinc acts as a sacrificial anode, which reacts with

corrosive reagents from the surroundings. A method to apply these films was developed by Paul

Jacques Malouin, who coated iron with zinc by dipping it into molten zinc in 1742.

For the preparation of thin films nowadays, two general concepts are of outstanding importance

and will be introduced in the following, (1) physical vapor deposition and (2) chemical vapor


68

deposition. These methods have a plethora of sub-methods and variations and the following

description of methods is by no means complete. Both methods are very powerful to prepare

thin films and are conducted at vacuum conditions, and the deposited thin film is transported

through the gas phase and deposited on a substrate.

Physical Vapor Deposition

The most common methods of physical vapor deposition are sputtering and evaporation

techniques. In sputtering techniques, atoms from a metal target are ejected by collisions of high

energetic particles, most commonly gas atoms. The ejected metal atoms are travelling from the

target to the substrate where they are condensing, forming a thin film. In physical evaporation

techniques, the target is heated to very high temperatures at very low pressures, leading to the

evaporation of atoms from the target. The evaporated atoms can then react with the substrate

and deposit on its surface forming a thin film. The advantages of these physical deposition

techniques are the ability to use nearly any kind of target and substrate. The biggest

disadvantage is the so called “line-of-sight-coverage” which makes the coverage of complex

samples with advanced geometrical features, e.g. protrusions unfeasible

Chemical Vapor Deposition

Chemical Vapor deposition summarizes all methods in which a chemical precursor is

decomposed and deposited on a surface. Many variations of this method exist, but the general

advantages of this method is the uniform coverage of complex shaped substrates. A big

drawback of this method is the limitation of precursors, not for every kind of coating suitable

precursor molecules have been developed. A very useful variation of this method, which will

be the focal point in the following is atomic layer deposition, or short ALD.


69

5.2 Atomic Layer Deposition

The fabrication of highly conformal thin films of metal or metal oxides are of eminent

importance for the production of modern devices in electronics and nanotechnology. There are

various methods to prepare thin films, the most common used techniques are either physical or

chemical methods. For instance, The most common methods to prepare cobalt oxide thin films

are for example sol-gel processes,1-3 spray pyrolysis,4-7 electrodeposition and physical vapor

deposition (PVD).8-12 The precision of these methods is still limited and hence the development

of new deposition techniques for these films is necessary. Up to date, the most promising

methods, which outperform the afore mentioned by means of film thickness and phase purity

are chemical vapor deposition (CVD) and atomic layer deposition (ALD).13 Among these

techniques, specifically ALD is a very powerful method to deposit films which possess

exceptional conformality and distinct morphology and phase control on the nanometer scale is

possible.9-10 Furthermore, the deposition of thin films on complex-shaped substrates is possible

by this method.

ALD also called ALE (atomic layer epitaxy) was developed in the 1970s by T. Suntola and J.

Antson to deposit thin films from the chemical vapor phase. The ALD process allowed

producing high quality, uniform and conformal thin films over large and complex-shaped areas

with precise control of thickness. These characteristic function of ALD has caught an enormous

attention from the microdevice and semiconductor industries. Fundamental studies as well as

todays application fields of ALD have been excellently reviewed in several reports by T.

Suntola, L. Niinistö, M. Leskelä, M. Ritala.14-20

ALD is considered as an advanced version CVD, because ALD shows two unique features

compared to CVD processes. ALD is a thin film deposition technique, which relies on


70

sequential and self-limiting surface reactions in the gas phase. The precursor reacts with the

surface of the substrate as well as the surface created by the complementary reactant in a self-

limiting and alternating fashion which leads to a discontinuous process while CVD provides a

simultaneous process via thermally induced decomposition of precursors on the surface.

Figure 5.1 Schematic illustration of the ALD reaction cycle


71

Unlike precursors used for CVD growth, an ALD precursor should be thermally stable at

deposition temperature to guarantee the self-limiting saturation of the surface. (Criteria of ALD

precursors will be discussed in detail in chapter 5.3) Full ALD cycles consist of metal

containing precursor and the complementary reactant. In the first step, the surface (most likely

OH groups on the surface) is exposed to a pulse of gaseous metal-containing precursor and

saturated by the precursor via chemisorption which inhibits the further growth (Figure 5.1a).

Excess precursor and by-products are purged out with an inert gas (e.g. nitrogen) (Figure 5.1b).

The resulting chemisorbed layer from the first step, is then exposed to the second

complementary reactant (e.g. H2O, O2, O3 H2, NH3 etc) (Figure 5.1c). This leads to the

formation of the desired material (for instance metals, metal oxides or metal nitrides depending

on the second reactant) and the excess of reactants and reaction by-products are subsequently

purged by inert gas. (Figure 5.1d) Repetition of these steps initiates the film growth restrained

by saturative and self-limiting surface reactions leading to uniform, conformal and precisely

controlled thickness (simply tuning the applied number of cycles controls film thickness).


72

Figure 5.2 Possible film growth behavior of ALD growth per cycles versus deposition

temperature.

To obtain an ideal ALD grown thin film, an optimized deposition temperature (Tdep) is required.

The temperature range where a constant growth rate is achieved is the so-called ALD window

(Figure 5.2).21 At temperatures below the ALD window the precursor either condenses on the

surface, or the surface reaction remains incomplete, due to the low temperature. Above the ALD

temperatures window, the precursors can decompose on the surface, which will lead to a CVD

like film growth or the surface species desorbs again.

The presence of an ALD window and the linearity of the thickness vs number of applied cycles

are typical features of the self-limiting character, however, it does not necessarily guarantee the

self-limiting growth process will actually take place. Only saturation studies with the growth

rate as a function of the precursor pulses finally demonstrate the self-limiting process.

5.3 ALD of metal oxides thin films

5.3.1 Precursors

Although atomic layer deposition techniques are widely used to provide very uniform and

conformal thin films, suitable and effective precursors remain scarce. Precursors employed for

ALD require several conditions. The criteria of ALD precursors are as follow. 1) Highly

reactive towards the functionalities on the surface as well as the surface prepared by the

complementary reactant. Furthermore, a complete reaction is desired. 2) Volatile (vapor

pressure > 0.1 Torr;)22-23 and thermally stable at growth (> seconds) and sublimation

temperatures (> months). Evaporation should occur in a single step without thermal


73

decomposition. 3) Non-reactive and non-corrosive byproduct formation is strongly preferred.

As is often the case, the reactive by-products can damage the film materials by etching or

reabsorption onto the reactive sites of the surface, thereby inducing non-uniformity and low

growth rates.23

ALD precursors can occur in the solid, liquid or gaseous state, but solid precursors own certain

drawbacks as unwanted particles might be transported by the carrier gas and incorporated into

the films. This in turn might cause defects in the films. Thus, the liquid or gaseous precursors

are preferred particularly in industrial scale application, if those are accessible.

Chronological development of precursors including metal halides, cyclopentadienyls (Cps),

alkoxides, -ketonates, alkylamides, trimethylsilanes (TMS), heteroleptic compounds of

mixture of theses ligands.

Figure 5.3 shows a list of the common ligands used for ALD precursors. In the following

chapters, the ALD precursors properties in detail will be discussed.


74

Figure 5.3 Outlook of ligand system used as precursors for metal oxides ALD. (dmap:

dimethylaminopropoxide, DAD: diazadienyl)


75

A. Metal halides

The metal halides with the general formula MXn (X = F, Al, Br or I; n = depends on the

oxidation state of metals) have the general advantage of stability at a broad range of

temperatures and a high reactivity. However, metal halides produce HX which is a strong acid

can damage or etch the surface of the metal/metal oxide thin films and this cause the

inhomogeneous film thickness. Moreover, metal halides precursors are not preferred in many

occasions in particular in our group due to the resulting halogen contamination.

B. ß-diketonates

Metal ß-diketonates with the general formula of M(thd)n (thd = 2,2,6,6-tetramethyl-3,5-

heptanedionyl) are one of the most common precursors used for gas phase depositions and

nearly every corresponding transition metal complexes across the periodic table as well as rare

earth metals compounds have been explored.24-25 The synthesis is relatively easy and straight

forward and very often they are commercially available. Owing to four strong M−O bonds in

the structure (low basicity of the ß-diketonate ligand), metal ß-diketonates possess low

reactivity towards water. Thus, metal ß-diketonates are rather developed for CVD precursor or

ALD with powerful oxidant such as ozone to combust the ligands. Metal ß-diketonates have

relatively low volatility and evaporation late but they have very high thermal stability (>

300 °C). Although metal ß-diketonates are the most intensively used precursor, they cause the

major problems concerning the low growth rates (0.2 – 0.4 Å/cycle), high quantity of residue

related to the high evaporation temperature due to the high thermal stability.26 [Andrian 167,168]


76

C. Amidinates

The bidendate chelating effects of amidinates improve the thermal stability which is the major

drawback of many monodendate alkylamides. Moreover, easily tunable steric crowding in the

ligand sphere of the system prevents the oligomerization, which has a huge impact on the

volatility of the compounds. In fact, the presence of two substituents (NR2) at the nitrogen atom

readily leads to a distinct increase of steric hindrance compared to oxygen based systems

(OR).27-28 Also amidinates have good reactivity towards oxidizing reagent in the ALD process

such as water and ozone. Amidinates were intensively investigated which diminish the

drawbacks of conventional precursors. Although numerous amidinates have been reported, only

a few ALD process are known for the preparation of metal oxides.29 Details of amnidinates

synthetic route and their electronic structures will be dicussed in the following chapter in

comparison to the guanidinates. (See 1.2.1.7 Guanidinates)

D. Guanidinates

Guanidinates are closely related to the amidinates regarding the tunability of their steric

hindrance, sturcture and bidendate chelating effect, however guanidinates possess an extended

electronic flexibility since the lone pair electrons of the amido-nitrogen is delocalized in the

ligand -system.30-32 Additionally, guanidinate ligands are stronger bases in comparison to the


77

amidinates, which increases the reactivity of the corresponding guanidinato metal complexes.

As an ALD precursor, these features give rise to advantages, in particular from the increase of

reactivity towards hydroxyl groups on the surface leading to a high surface coverage and high

growth rates.

Amidinate and guanidinate compounds, particularly Group 13 and transition metals are

investigated intensively. Synthetic strategies to prepare metal guanidinate complexes include

several different routes, most common approaches are summarized in the following.30, 33

(a) Salt metathesis reaction

The principle of salt metathesis reaction is the chemical process of the exchange of cations

between a metal halide and an alkali metal (mostly Li or Na) guanidinates. This approach

includes a two-step reaction, where an alkali metal guanidinate [Li(NR’}2CNR2]x is created by

insertion of carbodiimide into the alkyl lithium amide. Normally this step is a quantitative

reaction, [Li(NR’)2CNR2]n is not separated but its solution (most of the case Et2O) is used

directly for the next step. In the second step, reaction with metal halides give the metal

guanidinates with the general formula of [Mn(NR’)2CNR2]n (n is related to the oxidation state

of the metals) and LiCl as a byproduct.30, 34-35 (Scheme 1) This synthetic route is most common

way to synthesize the metal guanidinates. Reaction of dialkylamide and N,N’-dialkyl-

carbodiimide gives almost quantitative yield of lithiated guanidinato complex, normally metal

halides are added in-situ without isolation of lithiated guanidinate.


78

Scheme 5.1 Synthetic scheme of metal guanidinates via salt metathesis reaction. R, R’ = alkyl

or aryl group, MXn = metal halides.

(b) Insertion of carbodiimide into a metal−amide bond

It is known that, N,N’-dialkylcarbodiimides cleave the bond between metal and nitrogen in alkyl

amides (M−NR2) and are inserted into the M−NR2 bonds.32, 36-37 A lone pair electron of the

nitrogen atom in the dialkyl-carbodiimide attacks the metal center, then the dialkylamido (NR2)

ligands from the metal migrates into the carbon of the dialkyl-carbodiime forms an intermediate

state where the guanidinate moiety coordinates to the metal center in a monodendate fashion.

Consequently, the other nitrogen atom from the dialkyl-carbodiimide coordinates to the metal

center to form the final chelating metal guanidinate complex. (Scheme 2)


79

Scheme 5.2 Mechanistic procedure of the insertion and rearrangement of dialkyl-carbodiimide

into a metal-amide bond.37

E. Oxygen sources

In metal oxide thin film process, the oxygen source is needed for oxidation of the metal

precursor. H2O, O2 and O3 are by far the most commonly adopted oxygen sources for oxide

processes.


80

5.3.2 Transition metal oxides and cobalt

Transition metal oxides are known to exhibit distinctive physical/chemical properties including

electric/optical and catalytic/semiconductive properties due to the concurrence of delocalized

and localized d-electrons. Notwithstanding, the performance of those properties are highly

related to the morphology, structure and impurities of the materials. These properties can be

reasoned by the band structure of transition metal oxides. The bulk band structure of transition

metal oxides consists of overlapping p-orbitals from the oxygen atoms. These orbitals are highly

populated and of comparatively low energy, forming the valence band. Additionally, the d-

orbitals of the metals are also overlapping, although they are only sparsely populated thus

forming the conduction band. This band is of higher energy than the valence band and the

energy difference is called band gap. This band gap prevents the recombination of electron-hole

pairs which are separated into the valence and conduction band. Exactly this separation allows

the charge transfer onto adsorbed surface species, a requirement for using transition metal

oxides in a manifold of catalytic processes.

Owing to its peculiar and versatile physical/chemical properties of cobalt oxides such as

electrochemical capacitors, high energy density as Li ion batteries, oxygen evolution reaction

(OER) catalyst, optical gas sensors as well as their abundacy in earth, they have attracted

substantial attention from the material scientists. In general, cobalt oxide exists in three different

forms, CoIIO, CoIII2O3 and CoII,III

3O4 and the latest stoichiometry is predominantly studied for

the applications due to its chemical stability and electrochemical properties.6 The focus in this

thesis will lay on the description of cobalt-oxide materials in particular the mixed valent CoII

CoIII containing spinel Co3O4. Co3O4 is studied in the field of water splitting system as an


81

effective photoelectrocatalyst. The water splitting system consists two half reactions: namely

hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and the latter reaction

is the rate-determining step because it requires the coupling of four electrons and four proton

transfers and formation of O−O bond which normally demands high overpotential to initiate

the reaction.38 The Co3O4 unit cell has a spinel structure and direct optical band gap of 1.4-2

eV in the bulk solid state. However, nanostructured Co3O4 shows considerably larger band gap

(ca 2.5 eV).39 A prerequisite for the high activity in OER is the presence of two distinct cobalt

sites in spinel Co3O4. There are tetrahedrally coordinated Co2+Td sites and octahedrally

coordinated Co3+Oh sites.40 It was shown in different studies, that the OER reaction is highly

dependent on the nature of the exposed surface sites, which in turn are interacting with adsorbed

species. The importance of both sites remains controversially discussed in the literature, even

though, both sites are important as they are building up the geometrical environment for the

catalytically active site. In a study by Wang et al. the dependence of the OER on both metal

sites was probed using an ion substitution technique. They used CoAl2O4 only containing

Co2+Td sites as well as ZnCo2O4, which only contains Co3+

Oh sites. From their study using in

operando spectroscopic methods it was revealed that the Co2+Td site is forming CoOOH species

during the reaction which is an important intermediate in the OER reaction, whilst the Co3+Oh

containing species remained catalytically inactive.40

Photocatalytic reactions often require a harsh alkali environment which result in a corrosion of

the layers, limiting the catalysis operation time.


82

6. References

1. Barrera, E.; Viveros, T.; Avila, A.; Quintana, P.; Morales, M.; Batina, N., Cobalt oxide

films grown by a dipping sol-gel process. Thin Solid Films 1999, 346, 138-144.

2. Armelao, L.; Barreca, D.; Gross, S.; Martucci, A.; Tieto, M.; Tondello, E., Cobalt oxide-

based films: sol–gel synthesis and characterization. J. Non-Cryst. Solids 2001, 293–295, 477-

482.

3. Quinlan, F. T.; Vidu, R.; Predoana, L.; Zaharescu, M.; Gartrner, M.; Groza, J.; Stroeve,

P., Lithium Cobalt Oxide (LiCoO2) Nanocoatings by Sol−Gel Methods. Ind. Eng. Chem. Res.

2004, 43, 2468-2477.

4. Athey, P. R.; Urban, F. K.; Tabet, M. F.; McGahan, W. A., Optical properties of cobalt

oxide films deposited by spray pyrolysis. J. Vac. Sci. Technol., A 1996, 14, 685-692.

5. Shinde, V. R.; Mahadik, S. B.; Gujar, T. P.; Lokhande, C. D., Supercapacitive cobalt

oxide (Co3O4) thin films by spray pyrolysis. Appl. Surf. Sci. 2006, 252, 7487-7492.

6. Louardi, A.; Rmili, A.; Ouachtari, F.; Bouaoud, A.; Elidrissi, B.; Erguig, H.,

Characterization of cobalt oxide thin films prepared by a facile spray pyrolysis technique using

perfume atomizer. J. Alloy. Compd. 2011, 509, 9183-9189.

7. Abbas, T. A.-H.; Slewa, L. H.; Khizir, H. A.; Kakil, S. A., Synthesis of cobalt oxide

(Co3O4) thin films by electrostatic spray pyrolysis technique (ESP). J. Mater. Sci. Mater.

Electron. 2016, 1-7.

8. Meyer, W.; Biedermann, K.; Gubo, M.; Hammer, L.; Heinz, K., Surface structure of

polar Co3O4 (111) films grown epitaxially on Ir(100)-(1 × 1). J. Phys. Condens. Matter 2008,

20, 265011.

9. Ngo, T. Q.; Posadas, A.; Seo, H.; Hoang, S.; McDaniel, M. D.; Utess, D.; Triyoso, D.

H.; Buddie Mullins, C.; Demkov, A. A.; Ekerdt, J. G., Atomic layer deposition of photoactive


83

CoO/SrTiO3 and CoO/TiO2 on Si(001) for visible light driven photoelectrochemical water

oxidation. J. Appl. Phys. 2013, 114, 084901.

10. Johnson, R. W.; Hultqvist, A.; Bent, S. F., A brief review of atomic layer deposition:

from fundamentals to applications. Mater. Today 2014, 17, 236-246.

11. Mazzi, A.; Bazzanella, N.; Orlandi, M.; Edla, R.; Patel, N.; Fernandes, R.; Miotello, A.,

Physical vapor deposition of mixed-metal oxides based on Fe, Co and Ni as water oxidation

catalysts. Mater. Sci. Semicond. Process. 2016, 42, Part 1, 155-158.

12. Xu, T.; Schwarz, M.; Werner, K.; Mohr, S.; Amende, M.; Libuda, J., Structure-

Dependent Anchoring of Organic Molecules to Atomically Defined Oxide Surfaces: Phthalic

Acid on Co3O4(111), CoO(100), and CoO(111). Chem. Eur. J. 2016, 22, 5384-5396.

13. Klepper, K. B.; Nilsen, O.; Fjellvåg, H., Growth of thin films of Co3O4 by atomic layer

deposition. Thin Solid Films 2007, 515, 7772-7781.

14. Leskelä, M.; Ritala, M., Atomic Layer Deposition Chemistry: Recent Developments

and Future Challenges. Angew. Chem. Int. Ed. 2003, 42, 5548-5554.

15. Leskelä, M.; Ritala, M., Rare-earth oxide thin films as gate oxides in MOSFET

transistors. J. Solid State Chem. 171, 170-174.

16. Tuomo Suntola, J. H., Atomic Layer Epitaxy. Annual Review of Materials Science 1985,

15, 177-195.

17. Suntola, T., Atomic layer epitaxy. Materials Science Reports 1989, 4, 261-312.

18. Suntola, T., Surface chemistry of materials deposition at atomic layer level. Appl. Surf.

Sci. 1996, 100, 391-398.

19. Niinistö, L., Atomic layer epitaxy. Current Opinion in Solid State and Materials Science

1998, 3, 147-152.

20. Niinistö, L.; Päiväsaari, J.; Niinistö, J.; Putkonen, M.; Nieminen, M., Feature Article:

Advanced electronic and optoelectronic materials by Atomic Layer Deposition: An overview


84

with special emphasis on recent progress in processing of high-k dielectrics and other oxide

materials. physica status solidi (a) 2004, 201, 1375-1375.

21. Adelmann, C.; Delabie, A.; Schepers, B.; Rodriguez, L. N. J.; Franquet, A.; Conard, T.;

Opsomer, K.; Vaesen, I.; Moussa, A.; Pourtois, G.; Pierloot, K.; Caymax, M.; Van Elshocht,

S., Atomic Layer Deposition of Tantalum Oxide and Tantalum Silicate from Chloride

Precursors. Chem. Vap. Deposition 2012, 18, 225-238.

22. Mikko Ritala, M. L., Handbook of Thin Films Materials: Deposition and Processing of

Thin Films. In Handbook of Thin Films, Nalwa, H. S., Ed. Academic Press: Burlington, 2002;

Vol. 1.

23. Ritala, M.; Niinisto, J., Chapter 4 Atomic Layer Deposition. In Chemical Vapour

Deposition: Precursors, Processes and Applications, The Royal Society of Chemistry: 2009;

pp 158-206.

24. Tiitta, M.; Niinistou, L., Volatile Metal β-Diketonates: ALE and CVD precursors for

electroluminescent device thin films. Chem. Vap. Deposition 1997, 3, 167-182.

25. Binnemans, K., Chapter 225 - Rare-earth beta-diketonates. In Handbook on the Physics

and Chemistry of Rare Earths, Karl A. Gschneidner, J.-C. G. B.; Vitalij, K. P., Eds. Elsevier:

2005; Vol. Volume 35, pp 107-272.

26. Luten, H. A.; Rees, W. S.; Goedken, V. L., Preparation and structural characterization

of, and chemical vapor deposition studies with, certain yttrium tris(β-diketonate) compounds.

Chem. Vap. Deposition 1996, 2, 149-161.

27. Lim, B. S.; Rahtu, A.; Park, J.-S.; Gordon, R. G., Synthesis and Characterization of

Volatile, Thermally Stable, Reactive Transition Metal Amidinates. Inorg. Chem. 2003, 42,

7951-7958.


85

28. Milanov, A. P.; Thiede, T. B.; Devi, A.; Fischer, R. A., Homoleptic Gadolinium

Guanidinate: A Single Source Precursor for Metal−Organic Chemical Vapor Deposition of

Gadolinium Nitride Thin Films. J. Am. Chem. Soc. 2009, 131, 17062-17063.

29. Lim, B. S.; Rahtu, A.; Gordon, R. G., Atomic layer deposition of transition metals. Nat.

Mater. 2003, 2, 749-754.

30. Bailey, P. J.; Pace, S., The coordination chemistry of guanidines and guanidinates.

Coord. Chem. Rev. 2001, 214, 91-141.

31. Coyle, J. P.; Johnson, P. A.; DiLabio, G. A.; Barry, S. T.; Müller, J., Gas-Phase

Thermolysis of a Guanidinate Precursor of Copper Studied by Matrix Isolation, Time-of-Flight

Mass Spectrometry, and Computational Chemistry. Inorg. Chem. 2010, 49, 2844-2850.

32. Barry, S. T., Amidinates, guanidinates and iminopyrrolidinates: Understanding

precursor thermolysis to design a better ligand. Coord. Chem. Rev. 2013, 257, 3192-3201.

33. Musashi, Y.; Sakaki, S., Insertion of carbon dioxide into a rhodium(III)-hydride bond:

a theoretical study [dagger]. Journal of the Chemical Society, Dalton Transactions 1998, 577-

584.

34. Edelmann, F. T., Chapter 3 - Advances in the Coordination Chemistry of Amidinate and

Guanidinate Ligands. In Adv. Organomet. Chem., Anthony, F. H.; Mark, J. F., Eds. Academic

Press: 2008; Vol. Volume 57, pp 183-352.

35. Edelmann, F. T., Lanthanide amidinates and guanidinates: from laboratory curiosities

to efficient homogeneous catalysts and precursors for rare-earth oxide thin films. Chem. Soc.

Rev. 2009, 38, 2253-2268.

36. Chang, C.-C.; Hsiung, C.-S.; Su, H.-L.; Srinivas, B.; Chiang, M. Y.; Lee, G.-H.; Wang,

Y., Carbodiimide Insertion into Organoaluminum Compounds and Thermal Rearrangement of

the Products. Organometallics 1998, 17, 1595-1601.


86

37. Rowley, C. N.; DiLabio, G. A.; Barry, S. T., Theoretical and Synthetic Investigations

of Carbodiimide Insertions into Al−CH3 and Al−N(CH3)2 Bonds. Inorg. Chem. 2005, 44,

1983-1991.

38. Koper, M. T. M., Thermodynamic theory of multi-electron transfer reactions:

Implications for electrocatalysis. J. Electroanal. Chem. 2011, 660, 254-260.

39. Ramakrishnan, V.; Kim, H.; Park, J.; Yang, B., Cobalt oxide nanoparticles on TiO2

nanorod/FTO as a photoanode with enhanced visible light sensitization. RSC Adv. 2016, 6,

9789-9795.

40. Wang, H.-Y.; Hung, S.-F.; Chen, H.-Y.; Chan, T.-S.; Chen, H. M.; Liu, B., In Operando

Identification of Geometrical-Site-Dependent Water Oxidation Activity of Spinel Co3O4. J.

Am. Chem. Soc. 2016, 138, 36-39.


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6.

Low temperature atomic layer deposition of cobalt oxide

as an effective catalyst layer for photoelectrochemical

water splitting devices

Jiyeon Kim, Tomi Iivonen, Jani Hämäläinen, Marianna Kemell, Kristoffer Meinander,

Kenichiro Mizohata, Lidong Wang, Radim Beranek, Markku Leskelä, Anjana Devi

All contents of this paper have been published in Chem. Mater., 2017, 29 (14), 5796–5805.

Reprinted with permissions, Copyright © 2017 American Chemical Society.


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6. Low temperature atomic layer deposition of cobalt oxide as an

effective catalyst layer for photoelectrochemical water splitting

devices2

6.1 Abstract

We have developed a low-temperature atomic layer deposition (ALD) process for depositing

crystalline and phase pure spinel cobalt oxide (Co3O4) films at 120 °C using Co(tBu2DAD)2 and

ozone as co-reagent. X-ray diffraction, UV-Vis spectroscopy, atomic force microscopy, field

emission scanning electron microscopy, X-ray photoelectron spectroscopy and time-of-flight

elastic recoil detection analysis were performed to characterize the structure and properties of

the films. Full characterization of the film demonstrates that as-deposited Co3O4 films are

crystalline with low amount of impurities (<5 % hydrogen) despite low deposition temperatures.

Deposition of ultra-thin Co3O4 (< 1.1 nm) layers onto thin TiO2 films (100 nm) resulted in 30 %

improvement of photocurrent compared to pristine TiO2 films, demonstrating the applicability

of the developed ALD process for deposition of effective, conformal electrocatalytic layers in

photoelectrochemical water-splitting devices.

2 This chapter has been in part submitted for publication and is currently under revision.


89

6.2 Introduction

The interest in nanostructured cobal(II,III) oxide has been growing enormously over the past

few years, due to its gigantic potential for a variety of applications, in such areas as

electrochemistry, catalysis, sensing, batteries and energy storage.1-5 Co3O4 proved to be an

excellent electrocatalyst for water oxidation and is hence of outstanding importance, since the

water oxidation reaction remains the kinetic bottleneck in water splitting systems. Because of

that, CO3O4 catalysts are among the most favorable materials in this field, which is directly

connected to a sustainable and low-cost energy supply. 6-13 Electrocatalyst activity and their use

in thin-film devices (e.g. for chemical water splitting) generally depends on a variety of factors,

such as composition, morphology, thickness and optical properties.8, 14-17 The most common

methods to prepare cobalt oxide thin films are for example sol-gel processes,18-20 spray

pyrolysis,21-24 electrodeposition14 and physical vapor deposition (PVD).25-28 The precision of

these methods is still limited and hence the development of new deposition techniques for these

films is necessary. Up to date, the most promising methods, which outperform the afore

mentioned by means of film thickness and phase purity are chemical vapor deposition (CVD)

and atomic layer deposition (ALD).29 Among these techniques, specifically ALD is a very

powerful method to deposit films which possess exceptional conformality and distinct

morphology and phase control on the nanometer scale is possible. 26, 30 Furthermore, the

deposition of thin films on complex-shaped substrates is possible by this method. The before

mentioned benefits of ALD are in particular in the light of applicability of Co3O4 in devices of

marked importance. 31-33 These applications include for example the deposition of light

adsorbers, protective layers or catalysts film for photoelectrochemical water splitting devices.

34-39 Noticeably, only very few reports on the preparation of cobalt oxide exist, eventhough for

the deposition of other metal oxides ALD processes are quite common. Among the few


90

described ALD based routes towards cobalt oxides are for instance the deposition of cobalt

oxide from the cobalt amidinates precursor Co(iPrNCMeNiPr)2 in a water assisted ALD

process.30, 40 Other examples are the use of CoCp2 (Cp = cyclopentadienyl),11, 41 CCTBA

(dicobalthexacarbonyl-tert-butylacetylene),42 Co(thd)2 (thd = 2,2,6,6-tetramethylheptan-3,5-

dionate)29 and Co(acac)2 (acac = acetylacetonate)32, 43 combined with either O2 plasma or O3 as

the oxygen source. Drawbacks of these processes are however the high deposition temperatures

in combination with low film growth rates and impure thin films. 29, 32 Therefore, the

development of new cobalt precursors made from bidentate chelating ligands, for example

amidinates was an interesting alternative.44 By the bidentate binding of the amidinate

counteracts effects observed in monodentate compounds (i.e. amido or imido compounds),

particularly low thermal stability. At the same time, the all nitrogen coordinated amidinates

possess low deposition temperatures caused by the lower bond strength of M-N compared to

M-O.45 Remarkably, in the group of Winter, a amidinate build up from redox non-innocent

linkers was prepared, namely bis(1,4-di-tert-butyl-1,3-diazadiene) cobalt (II) Co(tBu2DAD)2.46

This kind of compound bear much higher redox activity under mild conditions. In a recent

report, a low temperature ALD process for the preparation of metallic Co0 films using formic

acid as a reducing agent and the before mentioned Co(tBu2DAD)2 was described. 5


91

6.3 Results and Discussion

2.3.1 Thermal properties of precursor [Co(tBu2DAD)2]

This chapter describes the development of a low temperature ALD process used for the

fabrication of phase pure Co3O4 thin films. The process employs [Co(tBu2DAD)2] as cobalt and

ozone as oxygen sources respectively. Additionally, it will be demonstrated that the prepared

films can be effectively used for the preparation of Co3O4/TiO2 electrocatalysts. TiO2 thin film

have gained massive attention and are utilized as protective layers in novel water splitting

devices.47-50

Scheme 6.1: Synthetic route towards [Co(tBu2DAD)2]

Scheme 6.1 depicts the synthesis route towards [Co(tBu2DAD)2], which was prepared in analogy

to the known procedure from the literature (Details Supporting Information). The precursor

shows very promising thermal properties, TGA/DTA and isothermal TG studies are presented

in Figure 6.1. Thermogravimetric studies of [Co(tBu2DAD)2] show a single step weight loss

with an onset at 160 °C. The residual mass is very low and accounts to 4 % of the initial mass.

Differential Thermal Analysis (DTA) reveals a melting point of 175 °C, which is in line with

the previously reported value (174-175 °C).46 The conducted isothermal studies show a linear

weight loss, and constant evaporation rate over a time range of 180 minutes. This makes them


92

suitable candidates as ALD precursors and guarantees sustainable precursor transport into the

ALD reactor (Figure 1b).

Figure 6.1 Thermal properties of Co(tBu2DAD)2, TGA/DTA (a) and isothermal TG studies (b)

measured at 100 – 120 °C.

The average of the slope of the isothermal studies was used to determine the evaporation rates

of the precursors at different temperatures. The obtained values are 2.52 µg/min (100 °C), 5.17

µg/min (110 °C) and 11.14 µg/min (120 °C). 100 °C was choosen as the evaporation

temperature for the deposition experiments. In order to maintain a thermal gradient between

precursor source and substrate chamber, the evaporation temperature was set to 95 °C.


93

6.3.2 Film Deposition

In order to verify the ALD growth of Co3O4, the deposition temperature, the precursor pulse

lengths of Co(tBu2DAD)2/O3 and the number of deposition cycles were varied (Figure 6.1). In

Figure 6.1a the growth rate is depicted as a function of temperature in the range 100 – 150 °C.

The temperature window with a constant growth rate is very narrow (110 − 120°C), which has

been observed for other ozone assisted metal oxide ALD proceses at high temperatures, due to

decomposition of ozone on the metal oxide surface.51-52 At deposition temperatures higher than

120 °C full coverage was not feasible over the whole substrate, due to the configuration of the

used F-120 reactor. Using 40 mm Si trenches, fully conformal Co3O4 deposition was also not

achieved, although 6 s pulses and 10 s purge times were used for both precursors. An

explanation for not reaching conformal depositions in the trenches are the ozone decomposition

of Co3O4 and the large surface area of the trench substrate. Hence, 120 °C were chosen as the

ideal deposition temperature for all further experiments (See Appendix, Figure 6.9).

After 2 second pulses of Co precursors followed by 2 sec nitrogen purges saturation of film

growth was observed (Figure 6.2b). For O3 saturation was also found to occur after 2 second

ozone purges. These findings are proof for the self-limiting character of the deposition at a

temperature of 120 °C. Noticeably, the linear dependence of the film thickness on the number

of deposition cycles further underlines the occurrence of a typical ALD process. Astonishingly,

the determined growth rate of 1.1 Å/cycle is five times higher than the previously reported

Co3O4 ALD deposition rate (0.25 Å/cycle, CoCp2/O3 ALD Window 110-300 °C).29This rate is

also slightly higher as recently found results, which used a different cobalt precursor

(diazadienyl Co precursor) and O3 as well as O2 as oxygen sources.53


94

Figure 6.2 Growth per cycle (GPC) as a function of (a) deposition temperature, (b)

[Co(tBu2DAD)2] pulse length, (c) ozone pulse length. (d, black line) Film thickness as a function

of number of applied cycles. The R2 value for a goodness of fit is 0.99967. (d, blue line) Average

rms roughness as a function of number of applied cycles. Films were grown with 300 cycles

using 2 s pulses and purges for both [Co(tBu2DAD)2] and ozone and deposition temperature 120

°C unless otherwise noted.


95

6.3.3 Film Characterization

A. Structure and Morphology

In order to determine the structure and the composition of the prepared Cobalt oxide thin films,

X-ray diffraction measurements, FESEM and atomic force microscopy measurements were

performed.

The X-ray diffraction measurements were performed in grazing incidence mode and are shown

in Figure 3. The films deposited at 120 °C are of polycrystalline nature and the reflections

found can be attributed to spinel cobalt lattice planes, namely the (111), (220), (311), (222),

(400), (511) and (440) planes.54 Already for the as-deposited films high intensities indicating

high crystallinity can be observed, which is in strong contrast to previously reported, much less

crystalline Co3O4 thin films prepared by ALD. 29, 53, 55 High Temperature XRD showed in air

and nitrogen atmosphere an increase in crystallinity in the range from room temperature to 700

°C. However, in oxygen free environment a reduction of the prepared Co3O4 thin films to CoO

was observed. This was indicated by new Bragg reflections fitting to the (111), (200) and (220)

lattice planes of periclase CoO. 56


96

Figure 6.3 HTXRD patterns of Co3O4 films deposited over 1000 cycles at 120 °C in a) air b)

nitrogen. The measurement temperature is shown under each diffractogram.

Via FSEM and AFM the surface morphology of the as-deposited films was analyzed. In Figure

6.4a and b the SEM and AFM images of the Co3O4 films deposited at 120 °C over 1000 cycles

are displayed. It is visible in both figures that homogeneous, well defined nano crystallites were

deposited without the necessity of any post annealing processes. The grain size of the nano

crystallites were in a range of 75 – 90 nm. In Figure 6.4c roughness studies with increasing

number of deposition cycles are depicted. Noticeably, the Surface average Rq values rise

linearly with the number of applied deposition cycles, with values of 0.81 nm, 1.1nm, 2.2 nm

and 3.3 nm for 150, 300, 600 and 1000 deposition cycles respectively (dependency of roughness

on number of cycles depicted in Figure 6.4c).


97

Figure 6.4 (a) Plane-view SEM and (b) representative AFM images of Co3O4 thin film

deposited over 1000 cycles at 120 °C. (c) AFM topographs of Co3O4 thin films deposited over

different cycles at 120 °C and the corresponding Rq values.

B. Film Composition

To confirm the chemical composition and the surface properties of the Co3O4 films prepared

at 120 °C over 1000 cycles, XPS and ToF-ERDA measurements were conducted. The XPS

measurements were performed in order to analyze the chemical states of surface cobalt and

oxygen in the prepared samples. In Figure 6.5 the survey spectrum of CO3O4 deposited on

Si(100) is depicted. Figure 6.5a shows the core level spectrum of Co 2p, which indicates spin

orbit splitting into 2p1/2 and 2p3/2. The plateau shake-up peaks confirm the presence of a

mixed Co2+/3+ oxidation state. From the satellite line tit is possible to make a distinction

between Co2+ and Co3+ states. Pure Co2+ shows a projecting shake-up peak within the areas of

786 and 790 eV. For Co3+ this shake-up peak can be found at 790 eV. 57 Because the 2p1/2 and

2p3/2 components contain identical chemical information, the 2p3/2 peak was chosen for curve

fitting and qualitative analysis, due to higher intensity. The binding energy peaks at 779.6 and

781.1 eV strongly suggest the presence of Co3+ and Co2+ species within the sample and the

shake up peaks belonging to these peaks can be found at 786.0 and 789.7 eV. 57-59 At 782.7

eV a peak that can be ascribed to Co(OH)2 is identified, which suggests the presence of this

species at the surface. 57 The O1s area also shows two peaks, one located at 531.3 eV and

529.6 eV. The first one is attributed to the lattice oxygen present in spinel Co3O4 and the latter

arises from hydroxyl groups present in Co(OH)2.


98

Figure 6.5 XPS Co 2p3/2 and O 1s photoelectron spectra of Co3O4 thin film (thickness 110

nm) deposited at 120 °C.

Depths profiles and Co:O ratios were provided by ToF-ERDA. One of the marked benefits of

this methods is its ability to quantitavively detect light elements including hydrogen which

cannot be detected using Rutherford backscattering Spectrometery (RBS), making it a powerful

method in combination with XPS measurements. The measurements proved that the films

contain a substantial hydrogen content, although it is below 5%. Interestingly, the amount of

hydrogen is highest close to the surface, which can be explained by the presence of surface

hydroxyls which were also found via XPS (Figure 6.6 and Table 6.1).


99

Table 6.1 (left) and Figure 6.6 (right) ToF-ERDA depth profile of a Co3O4 film deposited over

1000 cycles at 120 °C

The ToF-ERDA measurement revealed only low impurities, with 1.6 atomic percent of carbon

in the sample. Furthermore, also the nitrogen impurity is neglectable with only 0.7 atomic

percent. The found Co:O ratio amounts to 0.7 and is in line with the expected ratio for spinel

Co3O4.

2.3.4 Film Photoelectrochemical Properties

Cobalt oxide has proven to be an excellent electrocatalyst for the oxygen evolution reaction,

which is a important process in all photocatalytic water splitting devices. 60 Remarkably, the

disordered heterogenite structure of CoO(OH) has shown the highest activity among cobalt-

based electrocatalysts. 14, 16, 61-62 The simultaneous presence of hydroxylated Co2+ and Co3+ at

the surface of the thin films as previously discussed, strongly suggests that the highly active

CoO(OH) species is formed under electrocatalytic conditions.16 To confirm the applicability of


100

the prepared cobalt oxide thin films for water splitting, ultrathin films (1.1 nm) of the material

were deposited on 100 nm thick TiO2 layers on FTO glass substrate. For future

photoelectrochemical water splitting systems these composite TiO2/Co3O4 composites are of

very high interest. This is because currently TiO2 film are in the focus of research as highly

effective protection layers for low-gap semiconductors including Si, GaAs, Gap and CdTe.

These semiconductors usually undergo severe photocorrosion.47-50

The photoaction spectra (Figure 6.7) as well as the spectra under simulated solar light (Figure

6.8) show a striking increase of the photocurrent response of 30% in comparison to pristine

TiO2. Notably, the improvement excludes the presence of any harmful surface defect states in

TiO2 caused by the ALD-grown Co3O4. These effects could lead to enhanced surface

recombination. It is noticeable that the charge separation is enhanced, because the Co3O4

effectively extracts the holes from TiO2. This finally leads to the observed dramatic increase of

photocurrent. 63 Additionally, another advantage of Co3O4 is its role in the passivation of surface

states in TiO2, which has been recently reported for some photoanodes based on Fe2O3 or

BiVO4. 64-66 The photoholes in TiO2 have a highly positive nature and the presence of a co-

catalyst to induce full water oxidation under photoelectrochemical conditions is not necessary.

Therefore, the increased oxygen evolution rate can be compared to an enhancement of

photocurrent without a severe change in the faradaic oxygen evolution efficiency. Anyhow,

these results showcase that the developed low temperature ALD process is useful for the

preparation of electrocatalytic cobalt oxide layers on top of TiO2 layers. These TiO2 layers are

of crucial interest for the preparation of photoanodes for tandem water-splitting devices, which

are currently very susceptible towards photocorossion.47-50


101

Figure 6.7 Photocurrent transients under intermittent irradiation at different wavelengths (a)

and the corresponding photoaction spectrum (b) recorded in KOH (0.1 M) at 1.48 V vs. RHE

at TiO2 (100 nm) and TiO2/Co3O4 (10 cycles) photoanodes.

Figure 6.8 Photoelectrocatalytic properties of TiO2 (100 nm) and TiO2/Co3O4 (10 cycles)

photoanodes: (a) photocurrents (a) and oxygen evolution (b) during 1 hour irradiation by

simulated sunlight (Xenon lamp, AM1.5 filter, 100 mW/cm2) in borate buffer solution (0.1 M;

pH 9.2) at 1.25 V vs. RHE


102

6.4 Conclusion and Outlook

This chapter nicely demonstrates the possibility to deposit spinel cobalt oxide via ALD by using

an ozone assisted process with [Co(tBu2DAD)2]as a precursor. The process was conducted at

low temperatures (120 °C) and the obtained films are conformal, crystalline, phase pure and

only contain extremely low carbon and hydrogen contamination. A Post annealing treatment to

increase these films properties is not necessary. Furthermore, by the ALD process ultrathin

Co3O4 electrocatalyst films were prepared on top of TiO2 films, which lead to a striking

improvement of photoconversion efficiency. Due to the conformal nature of the ALD grown

films and the importance of TiO2 protective layers for photoelectrodes these finding will be of

very high relevance for the fabrication of a variety of solar water splitting devices.

6.5 Appindex

Thickness(nm) Top Middle Bottom

114 101 84

122 93 85

111 93 77

119 93 71


103

130 89 77

138 92 71

80

Average

thickness (nm) 122 94 78

Figure 6.9 SEM image of Si trench with an aspect ratio of 20:1 (depth 40 m, width 2 m).

Co3O4 film has been deposited over 1000 cycles at 120 °C using pulse lengths of 6 seconds

for both Co(tBu2DAD)2 and ozone. The purge length for both precursors was 10 seconds.

Fully conformal Co3O4 films could not be deposited on 40 m Si trenches (aspect ratio of

1:20) despite using 6 s pulse and 10 s purge times of both precursors. A conceivable

explanation of for not achieving full conformality in the trench structure is the combined

effect of ozone decomposing effect of Co3O4 and high surface area of the substrate.


104

Figure 6.10 XPS survey spectrum of Co3O4 thin film deposited over 1000 cycles at 120 °C.

Figure 6.10 displays the XPS survey scan of Co3O4 that is dominated by cobalt and oxygen

photopeaks. No Ar+ sputtering experiment was performed.


105

Figure 6.10 UV-Vis transmission spectrum and corresponding Tauc plot of Co3O4 thin film

deposited over 1000 cycles at 120 °C.

UV-Vis spectroscopy was performed on the as-deposited Co3O4 film grown on soda-lime

glass to determine the optical bandgap of Co3O4 thin films via Tauc plot. Obtained data

indicated a direct band gap value of 2.02 eV.


106

Figure 6.11 UV-Vis transmission spectra of TiO2 and Co3O4

UV-Vis spectroscopy was performed on pristine TiO2 (black line) and TiO2/Co3O4 (red line)

grown on FTO glass. As can be seen in Figure S5, the shift between pristine TiO2 and

TiO2/Co3O4 was not observed.


107

Figure 6.12 XRD patterns of TiO2 deposited at 275 °C over 2000 cycles on FTO glass

XRD reflections of TiO2 films deposited at 275 °C on FTO show mixed phases of

anatase/rutile dominanted by the anatase phase.72 (Figure S4)



108

6.5.1 Precursor synthesis

[Co(tBu2DAD)2] was synthesized modifying the literature reported procedure.46 All

manipulations were carried out in an atmosphere of argon purified by Cu catalysts and

molecular sieves using standard Schlenk and glove-box techniques. All solvents were dried

using an MBraun Solvent Purification System. The crude mixture after the synthesis was

sublimed at 60 °C in vacuo (10-3 mbar), then the temperature was gradually increased up to 90

°C to remove excess amount of free ligands. Deep dark- green crystals were collected on a

cooling finger by slow sublimation (100 °C, 10-3 mbar). The purity and the thermal properties

were analyzed using elemental analysis, mass spectrometry and thermogravimetric analysis

(TGA, EXSTAR 6000 TG/DTA 6200, Seiko Instruments Inc.). The measurements were

performed under inert gas atmosphere using nitrogen (99.999 %) at ambient pressure.

Approximately 10 mg of samples were filled in aluminum crucibles with a circular opening.

The heating rate was 5 °C/min and a nitrogen flow of 300 ml/min was used. For isothermal TG

studies, the sample was heated with a rate of 10 °C/min until the desired temperature was

reached, then mass loss was measured for 180 min at constant temperature.

EI-MS [m/z]: 395.3 [M]+, 380.2 [M]+-CH3, 338.2 [M]+-C(CH3)3, 227.1 [M]+-L, 212.1 [M]+-L-

CH3


109

6.5.2 Film deposition

Cobalt oxide thin films were deposited using a hot-wall flow-type ALD reactor (ASM

Microchemistry F-120) operated under a nitrogen atmosphere of approximately 5 mbar.

Nitrogen (99.999 %) was used as both carrier and purging gas. Si (100) and soda lime glass cut

to 5 × 5 cm2 pieces were used as substrates. Co(tBuDAD)2 was sublimed from an open glass

boat held inside the reactor at 95 − 100 °C. Ozone was produced from oxygen (99.999 %) using

a Weeco Ozomatic Modulator 4 HC Lab Ozone generator (ozone concentration of

approximately 100 g/Nm3) and introduced to the reactor using needle and solenoid valves. The

deposition temperature was varied from 100 – 150 °C. Thin films for photoelectrochemical

studies were prepared as follows: 100 nm TiO2 thin films were deposited on 1.5 x 2.0 cm2 FTO

substrates (Solems TEC7) by applying the TiOMe4 / H2O ALD process at 275 °C.67 The

TiO2/Co3O4 structure was obtained by applying 10 deposition cycles of the Co3O4 process at a

temperature of 120 °C.

6.5.3 Film characterization

All characterizations were conducted using films deposited over 300 cycles (film thickness of

approximately 30 nm) on Si (100) substrates unless otherwise noted. All thickness

measurements related to saturation studies and the effect of deposition temperature were done

on Si (100) with an in situ aluminum oxide layer deposited over 100 cycles using

trimethylaluminum (TMA) and ozone (Al2O3 film thickness of approximately 10 nm). The

purpose of the Al2O3 layer was to twofold: I) To produce a reproducible, hydroxylated starting

surface68 for each cobalt oxide film deposition and II) to cover and thus passivate cobalt oxide

that would grow on the ALD reactor walls and eventually cause ozone decomposition.52


110

Film thickness was measured with energy dispersive X-ray spectrometry (EDX). The EDX

spectra were collected using an Oxford INCA 350 microanalysis system connected to a Hitachi

S-4800 field emission scanning electron microscope (FESEM). Film thicknesses were

calculated from the EDX spectra using the GMRfilm software and assuming bulk density values

of 6.1 g cm-3 for the Co3O4 films.69

All X-ray diffraction measurements were performed in the grazing incidence (GI) geometry

using an incident angle of 1 °. Film crystal structure was identified GI-(XRD) patterns obtained

with a PANalytical X’Pert Pro MPD diffractometer. The high temperature XRD (HTXRD)

measurements were done using an Anton-Paar HTK1200N oven in both air and nitrogen

atmospheres. The nitrogen gas (99.999%) was purified in situ prior to the experiment in an

Entegris 35KF-I-4R gas purification system.

Film morphology was studied using both FESEM and atomic force microscopy (AFM). AFM

images were captured in tapping mode using a Veeco Multimode V tool equipped with a

Nanoscope V controller. Film roughness was calculated as average root mean square (Rq)

values from 2 x 2 µm2 images obtained using Si probes (RTESP, Bruker).

X-ray photoelectron spectra (XPS) were obtained using an Omicron ARGUS spectrometer

operated at a pass energy of 20 eV. Samples were illuminated with X-rays emitted from a

standard Mg source (K alpha line) at a photon energy of 1253.6 eV. No sputtering was done on

the films studied. Binding energies were calibrated using the C 1s peak of ambient hydrocarbons

(284.8 eV). Peak fitting was done using the CasaXPS software package.

The time-of-flight elastic recoil detection analysis (ToF-ERDA) measurements were done on

films deposited on Si (100) over 1000 cycles using a 50 MeV 127I7+ ion beam in a setup

described in full elsewhere.70


111

UV-Vis transmittance measurements were performed on films deposited on soda lime glass

substrates using a Hitachi U2000 spectrophotometer.

6.5.4 Photoelectrochemistry

Photocurrent measurements were carried out using a three electrode setup with a platinum

counter electrode and a Ag/AgCl (3M KCl) reference electrode using a SP-300 BioLogic

potentiostat. The photoelectrodes were pressed against an O-ring of the cell leaving an

irradiated area of 0.5 cm2. The electrodes were irradiated from the back side (through the FTO

glass). The monochromatic wavelength-

resolved photocurrent measurements were performed using a tunable monochromatic light

source (Instytut Fotonowy) provided with a 150 W Xenon lamp and a grating monochromator

with a bandwidth of 10 nm and SP-300 BioLogic potentiostat. The monochromatic intensities

between 300 nm and 800 nm were in the range of 0.16–2.48 mW/cm2. Appropriate cut-off filters

were used in order to eliminate the second-order diffraction radiation. The oxygen evolution

was monitored by an OxySense 325i oxygen analyzer in a two-compartment cell, and the

electrodes were irradiated by a 150 W Xenon lamp (LOT Oriel) equipped with a KG-3 (Schott)

heat-absorbing filter and an AM 1.5 filter. Prior to experiments the electrolyte solutions were

purged with argon for 30 minutes.


112

6.6 References

1. Švegl, F.; Orel, B.; Hutchins, M. G.; Kalcher, K., Structural and Spectroelectrochemical

Investigations of Sol‐Gel Derived Electrochromic Spinel Co3O4 Films. J. Electrochem. Soc.

1996, 143, 1532-1539.

2. Ando, M.; Kobayashi, T.; Iijima, S.; Haruta, M., Optical recognition of CO and H2 by

use of gas-sensitive Au-Co3O4 composite films. J. Mater. Chem. 1997, 7, 1779-1783.

3. Li, W. Y.; Xu, L. N.; Chen, J., Co3O4 Nanomaterials in Lithium-Ion Batteries and Gas

Sensors. Adv. Funct. Mater. 2005, 15, 851-857.

4. Bekermann, D.; Gasparotto, A.; Barreca, D.; Maccato, C.; Comini, E.; Sada, C.;

Sberveglieri, G.; Devi, A.; Fischer, R. A., Co3O4/ZnO Nanocomposites: From Plasma Synthesis

to Gas Sensing Applications. ACS Appl. Mater. Interfaces 2012, 4, 928-934.

5. Klesko, J. P.; Kerrigan, M. M.; Winter, C. H., Low Temperature Thermal Atomic Layer

Deposition of Cobalt Metal Films. Chem. Mater. 2016, 28, 700-703.

6. Lewis, N. S.; Nocera, D. G., Powering the planet: Chemical challenges in solar energy

utilization. Proc. Natl. Acad. Sci. 2006, 103, 15729-15735.

7. Dau, H.; Limberg, C.; Reier, T.; Risch, M.; Roggan, S.; Strasser, P., The Mechanism of

Water Oxidation: From Electrolysis via Homogeneous to Biological Catalysis. ChemCatChem

2010, 2, 724-761.

8. Trotochaud, L.; Mills, T. J.; Boettcher, S. W., An Optocatalytic Model for

Semiconductor–Catalyst Water-Splitting Photoelectrodes Based on In Situ Optical

Measurements on Operational Catalysts. J. Phys. Chem. Lett. 2013, 4, 931-935.

9. Yang, J.; Wang, D.; Han, H.; Li, C., Roles of Cocatalysts in Photocatalysis and

Photoelectrocatalysis. Acc. Chem. Res. 2013, 46, 1900-1909.


113

10. Peter, L. M., Photoelectrochemical Water Splitting. A Status Assessment.

Electroanalysis 2015, 27, 864-871.

11. Ager, J. W.; Shaner, M. R.; Walczak, K. A.; Sharp, I. D.; Ardo, S., Experimental

demonstrations of spontaneous, solar-driven photoelectrochemical water splitting. Energy

Environ. Sci. 2015, 8, 2811-2824.

12. Zhou, X.; Shen, X.; Xia, Z.; Zhang, Z.; Li, J.; Ma, Y.; Qu, Y., Hollow Fluffy Co3O4

Cages as Efficient Electroactive Materials for Supercapacitors and Oxygen Evolution Reaction.

ACS Appl. Mater. Interfaces 2015, 7, 20322-20331.

13. Chua, C. S.; Ansovini, D.; Lee, C. J. J.; Teng, Y. T.; Ong, L. T.; Chi, D.; Hor, T. S. A.;

Raja, R.; Lim, Y.-F., The effect of crystallinity on photocatalytic performance of Co3O4 water-

splitting cocatalysts. Phys. Chem. Chem. Phys. 2016, 18, 5172-5178.

14. Kanan, M. W.; Nocera, D. G., In Situ Formation of an Oxygen-Evolving Catalyst in

Neutral Water Containing Phosphate and Co2+. Science 2008, 321, 1072-1075.

15. Lin, F.; Boettcher, S. W., Adaptive semiconductor/electrocatalyst junctions in water-

splitting photoanodes. Nat. Mater. 2014, 13, 81-86.

16. Bergmann, A.; Martinez-Moreno, E.; Teschner, D.; Chernev, P.; Gliech, M.; de Araújo,

J. F.; Reier, T.; Dau, H.; Strasser, P., Reversible amorphization and the catalytically active state

of crystalline Co3O4 during oxygen evolution. Nat. Commun. 2015, 6, 8625.

17. Nellist, M. R.; Laskowski, F. A. L.; Lin, F.; Mills, T. J.; Boettcher, S. W.,

Semiconductor–Electrocatalyst Interfaces: Theory, Experiment, and Applications in

Photoelectrochemical Water Splitting. Acc. Chem. Res. 2016, 49, 733-740.

18. Barrera, E.; Viveros, T.; Avila, A.; Quintana, P.; Morales, M.; Batina, N., Cobalt oxide

films grown by a dipping sol-gel process. Thin Solid Films 1999, 346, 138-144.


114

19. Armelao, L.; Barreca, D.; Gross, S.; Martucci, A.; Tieto, M.; Tondello, E., Cobalt oxide-

based films: sol–gel synthesis and characterization. J. Non-Cryst. Solids 2001, 293–295, 477-

482.

20. Quinlan, F. T.; Vidu, R.; Predoana, L.; Zaharescu, M.; Gartrner, M.; Groza, J.; Stroeve,

P., Lithium Cobalt Oxide (LiCoO2) Nanocoatings by Sol−Gel Methods. Ind. Eng. Chem. Res.

2004, 43, 2468-2477.

21. Athey, P. R.; Urban, F. K.; Tabet, M. F.; McGahan, W. A., Optical properties of cobalt

oxide films deposited by spray pyrolysis. J. Vac. Sci. Technol., A 1996, 14, 685-692.

22. Shinde, V. R.; Mahadik, S. B.; Gujar, T. P.; Lokhande, C. D., Supercapacitive cobalt

oxide (Co3O4) thin films by spray pyrolysis. Appl. Surf. Sci. 2006, 252, 7487-7492.

23. Louardi, A.; Rmili, A.; Ouachtari, F.; Bouaoud, A.; Elidrissi, B.; Erguig, H.,

Characterization of cobalt oxide thin films prepared by a facile spray pyrolysis technique using

perfume atomizer. J. Alloy. Compd. 2011, 509, 9183-9189.

24. Abbas, T. A.-H.; Slewa, L. H.; Khizir, H. A.; Kakil, S. A., Synthesis of cobalt oxide

(Co3O4) thin films by electrostatic spray pyrolysis technique (ESP). J. Mater. Sci. Mater.

Electron. 2016, 1-7.

25. Meyer, W.; Biedermann, K.; Gubo, M.; Hammer, L.; Heinz, K., Surface structure of

polar Co3O4 (111) films grown epitaxially on Ir(100)-(1 × 1). J. Phys. Condens. Matter 2008,

20, 265011.

26. Johnson, R. W.; Hultqvist, A.; Bent, S. F., A brief review of atomic layer deposition:

from fundamentals to applications. Mater. Today 2014, 17, 236-246.

27. Mazzi, A.; Bazzanella, N.; Orlandi, M.; Edla, R.; Patel, N.; Fernandes, R.; Miotello, A.,

Physical vapor deposition of mixed-metal oxides based on Fe, Co and Ni as water oxidation

catalysts. Mater. Sci. Semicond. Process. 2016, 42, Part 1, 155-158.


115

28. Xu, T.; Schwarz, M.; Werner, K.; Mohr, S.; Amende, M.; Libuda, J., Structure-

Dependent Anchoring of Organic Molecules to Atomically Defined Oxide Surfaces: Phthalic

Acid on Co3O4(111), CoO(100), and CoO(111). Chem. Eur. J. 2016, 22, 5384-5396.

29. Klepper, K. B.; Nilsen, O.; Fjellvåg, H., Growth of thin films of Co3O4 by atomic layer

deposition. Thin Solid Films 2007, 515, 7772-7781.

30. Ngo, T. Q.; Posadas, A.; Seo, H.; Hoang, S.; McDaniel, M. D.; Utess, D.; Triyoso, D.

H.; Buddie Mullins, C.; Demkov, A. A.; Ekerdt, J. G., Atomic layer deposition of photoactive

CoO/SrTiO3 and CoO/TiO2 on Si(001) for visible light driven photoelectrochemical water

oxidation. J. Appl. Phys. 2013, 114, 084901.

31. Leskelä, M.; Ritala, M., Atomic Layer Deposition Chemistry: Recent Developments

and Future Challenges. Angew. Chem. Int. Ed. 2003, 42, 5548-5554.

32. Backman, L. B.; Rautiainen, A.; Lindblad, M.; Krause, A. O. I., The interaction of cobalt

species with alumina on Co/Al2O3 catalysts prepared by atomic layer deposition. Appl. Catal.,

A 2009, 360, 183-191.

33. Barreca, D.; Devi, A.; Fischer, R. A.; Bekermann, D.; Gasparotto, A.; Gavagnin, M.;

Maccato, C.; Tondello, E.; Bontempi, E.; Depero, L. E.; Sada, C., Strongly oriented Co3O4 thin

films on MgO(100) and MgAl2O4(100) substrates by PE-CVD. CrystEngComm 2011, 13,

3670-3673.

34. Liu, R.; Lin, Y.; Chou, L.-Y.; Sheehan, S. W.; He, W.; Zhang, F.; Hou, H. J. M.; Wang,

D., Water Splitting by Tungsten Oxide Prepared by Atomic Layer Deposition and Decorated

with an Oxygen-Evolving Catalyst. Angew. Chem. Int. Ed. 2011, 50, 499-502.

35. Paracchino, A.; Laporte, V.; Sivula, K.; Grätzel, M.; Thimsen, E., Highly active oxide

photocathode for photoelectrochemical water reduction. Nat. Mater. 2011, 10, 456-461.


116

36. Morales-Guio, C. G.; Tilley, S. D.; Vrubel, H.; Grätzel, M.; Hu, X., Hydrogen evolution

from a copper(I) oxide photocathode coated with an amorphous molybdenum sulphide catalyst.

Nat. Commun. 2014, 5, 3059.

37. Young, K. M. H.; Hamann, T. W., Enhanced photocatalytic water oxidation efficiency

with Ni(OH)2 catalysts deposited on [small alpha]-Fe2O3 via ALD. Chem. Commun. 2014, 50,

8727-8730.

38. Steier, L.; Luo, J.; Schreier, M.; Mayer, M. T.; Sajavaara, T.; Grätzel, M., Low-

Temperature Atomic Layer Deposition of Crystalline and Photoactive Ultrathin Hematite Films

for Solar Water Splitting. ACS Nano 2015, 9, 11775-11783.

39. Hajibabaei, H.; Zandi, O.; Hamann, T. W., Tantalum nitride films integrated with

transparent conductive oxide substrates via atomic layer deposition for photoelectrochemical

water splitting. Chem. Sci. 2016, 7, 6760-6767.

40. Lim, B. S.; Rahtu, A.; Gordon, R. G., Atomic layer deposition of transition metals. Nat.

Mater. 2003, 2, 749-754.

41. Lichterman, M. F.; Shaner, M. R.; Handler, S. G.; Brunschwig, B. S.; Gray, H. B.;

Lewis, N. S.; Spurgeon, J. M., Enhanced Stability and Activity for Water Oxidation in Alkaline

Media with Bismuth Vanadate Photoelectrodes Modified with a Cobalt Oxide Catalytic Layer

Produced by Atomic Layer Deposition. J. Phys. Chem. Lett. 2013, 4, 4188-4191.

42. Han, B.; Choi, K. H.; Park, K.; Han, W. S.; Lee, W.-J., Low-Temperature Atomic Layer

Deposition of Cobalt Oxide Thin Films Using Dicobalt Hexacarbonyl tert-Butylacetylene and

Ozone. Electrochem. Solid State Lett. 2011, 15, D14-D17.

43. Taheri Najafabadi, A.; Khodadadi, A. A.; Parnian, M. J.; Mortazavi, Y., Atomic layer

deposited Co/γ-Al2O3 catalyst with enhanced cobalt dispersion and Fischer–Tropsch synthesis

activity and selectivity. Appl. Catal., A 2016, 511, 31-46.


117



7951-7958.



46. Knisley, T. J.; Saly, M. J.; Heeg, M. J.; Roberts, J. L.; Winter, C. H., Volatility and High

Thermal Stability in Mid- to Late-First-Row Transition-Metal Diazadienyl Complexes.

Organometallics 2011, 30, 5010-5017.

47. Chen, Y. W.; Prange, J. D.; Duehnen, S.; Park, Y.; Gunji, M.; Chidsey, C. E. D.;

McIntyre, P. C., Atomic layer-deposited tunnel oxide stabilizes silicon photoanodes for water

oxidation. Nat. Mater. 2011, 10, 539-544.

48. Scheuermann, A. G.; Prange, J. D.; Gunji, M.; Chidsey, C. E. D.; McIntyre, P. C.,

Effects of catalyst material and atomic layer deposited TiO2 oxide thickness on the water

oxidation performance of metal-insulator-silicon anodes. Energy Environ. Sci. 2013, 6, 2487-

2496.

49. Hu, S.; Shaner, M. R.; Beardslee, J. A.; Lichterman, M.; Brunschwig, B. S.; Lewis, N.

S., Amorphous TiO2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water

oxidation. Science 2014, 344, 1005-1009.

50. Lichterman, M. F.; Carim, A. I.; McDowell, M. T.; Hu, S.; Gray, H. B.; Brunschwig, B.

S.; Lewis, N. S., Stabilization of n-cadmium telluride photoanodes for water oxidation to O2(g)

in aqueous alkaline electrolytes using amorphous TiO2 films formed by atomic-layer

deposition. Energy Environ. Sci. 2014, 7, 3334-3337.

51. Li, W.; Gibbs, G. V.; Oyama, S. T., Mechanism of Ozone Decomposition on a

Manganese Oxide Catalyst. 1. In Situ Raman Spectroscopy and Ab Initio Molecular Orbital

Calculations. J. Am. Chem. Soc. 1998, 120, 9041-9046.


118

52. Knoops, H. C. M.; Elam, J. W.; Libera, J. A.; Kessels, W. M. M., Surface Loss in Ozone-

Based Atomic Layer Deposition Processes. Chem. Mater. 2011, 23, 2381-2387.

53. Han, B.; Park, J.-M.; Choi, K. H.; Lim, W.-K.; Mayangsari, T. R.; Koh, W.; Lee, W.-J.,

Atomic layer deposition of stoichiometric Co3O4 films using bis(1,4-di-iso-propyl-1,4-

diazabutadiene) cobalt. Thin Solid Films 2015, 589, 718-722.

54. Will, G.; Masciocchi, N.; Parrish, W.; Hart, M., Refinement of simple crystal structures

from synchrotron radiation powder diffraction data. J. Appl. Crystallogr. 1987, 20, 394-401.

55. Nandi, D. K.; Manna, J.; Dhara, A.; Sharma, P.; Sarkar, S. K., Atomic layer deposited

cobalt oxide: An efficient catalyst for NaBH4 hydrolysis. J. Vac. Sci. Technol., A 2016, 34,

01A115.

56. Liu, J. F.; Yin, S.; Wu, H. P.; Zeng, Y. W.; Hu, X. R.; Wang, Y. W.; Lv, G. L.; Jiang, J.

Z., Wurtzite-to-Rocksalt Structural Transformation in Nanocrystalline CoO. J. Phys. Chem. B

2006, 110, 21588-21592.

57. Yang, J.; Liu, H.; Martens, W. N.; Frost, R. L., Synthesis and Characterization of Cobalt

Hydroxide, Cobalt Oxyhydroxide, and Cobalt Oxide Nanodiscs. J. Phys. Chem. C 2010, 114,

111-119.

58. Biesinger, M. C.; Payne, B. P.; Grosvenor, A. P.; Lau, L. W. M.; Gerson, A. R.; Smart,

R. S. C., Resolving surface chemical states in XPS analysis of first row transition metals, oxides

and hydroxides: Cr, Mn, Fe, Co and Ni. Appl. Surf. Sci. 2011, 257, 2717-2730.

59. Li, J.; Lu, G.; Wu, G.; Mao, D.; Guo, Y.; Wang, Y.; Guo, Y., Effect of TiO2 crystal

structure on the catalytic performance of Co3O4/TiO2 catalyst for low-temperature CO

oxidation. Catal. Sci. Tech. 2014, 4, 1268-1275.

60. Harriman, A.; Pickering, I. J.; Thomas, J. M.; Christensen, P. A., Metal oxides as

heterogeneous catalysts for oxygen evolution under photochemical conditions. J. Chem. Soc.

Faraday Trans. 1988, 84, 2795-2806.


119

61. Kanan, M. W.; Yano, J.; Surendranath, Y.; Dincă, M.; Yachandra, V. K.; Nocera, D. G.,

Structure and Valency of a Cobalt−Phosphate Water Oxidation Catalyst Determined by in Situ

X-ray Spectroscopy. J. Am. Chem. Soc. 2010, 132, 13692-13701.

62. Risch, M.; Ringleb, F.; Kohlhoff, M.; Bogdanoff, P.; Chernev, P.; Zaharieva, I.; Dau,

H., Water oxidation by amorphous cobalt-based oxides: in situ tracking of redox transitions and

mode of catalysis. Energy Environ. Sci. 2015, 8, 661-674.

63. Ramakrishnan, V.; Kim, H.; Park, J.; Yang, B., Cobalt oxide nanoparticles on TiO2

nanorod/FTO as a photoanode with enhanced visible light sensitization. RSC Adv. 2016, 6,

9789-9795.

64. Barroso, M.; Cowan, A. J.; Pendlebury, S. R.; Gratzel, M.; Klug, D. R.; Durrant, J. R.,

The Role of Cobalt Phosphate in Enhancing the Photocatalytic Activity of α-Fe2O3 toward

Water Oxidation. J. Am. Chem. Soc. 2011, 133, 14868-14871.

65. Cummings, C. Y.; Marken, F.; Peter, L. M.; Tahir, A. A.; Wijayantha, K. G. U., Kinetics

and mechanism of light-driven oxygen evolution at thin film α-Fe2O3 electrodes. Chem.

Commun. 2012, 48, 2027-2029.

66. Ma, Y.; Le Formal, F.; Kafizas, A.; Pendlebury, S. R.; Durrant, J. R., Efficient

suppression of back electron/hole recombination in cobalt phosphate surface-modified undoped

bismuth vanadate photoanodes. J. Mater. Chem. A 2015, 3, 20649-20657.

67. Pore, V.; Rahtu, A.; Leskelä, M.; Ritala, M.; Sajavaara, T.; Keinonen, J., Atomic Layer

Deposition of Photocatalytic TiO2 Thin Films from Titanium Tetramethoxide and Water. Chem.

Vap. Deposition 2004, 10, 143-148.

68. Goldstein, D. N.; McCormick, J. A.; George, S. M., Al2O3 Atomic Layer Deposition

with Trimethylaluminum and Ozone Studied by in Situ Transmission FTIR Spectroscopy and

Quadrupole Mass Spectrometry. J. Phys. Chem. C 2008, 112, 19530-19539.


120

69. Waldo, R. A., An iteration procedure to calculate film compositions and thicknesses in

electron-probe microanalysis. Microbeam Anal. 1988, 23rd, 310-14.

70. Jokinen, J.; Keinonen, J.; Tikkanen, P.; Kuronen, A.; Ahlgren, T.; Nordlund, K.,

Comparison of TOF-ERDA and nuclear resonance reaction techniques for range profile

measurements of keV energy implants. Nucl. Instr. Meth. Phys. Res. 1996, 119, 533-542.


121

Supporting Information

Jiyeon Kim,a Tomi Iivonen,b Jani Hämäläinen,b Marianna Kemell,b Kristoffer Meinander,c Kenichiro Mizohata,c Lidong Wang,a Jyrki Räisänen,c Radim Beranek,a,d Markku Leskelä,b Anjana Devia*

a) Inorganic Materials Chemistry, Chair of Inorganic Chemistry II, Ruhr-University Bochum, Universitätstr. 150, 44801 Bochum, Germany b) Laboratory of Inorganic Chemistry, Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland c) Division of Materials Physics, Department of Physics, University of Helsinki, P.O. Box 43, FI-00014 Helsinki, Finland d) Institute of Electrochemistry, Ulm University, Albert-Einstein-Allee 47, 89081 Ulm, Germany

Table of Contents

Figure S1 EI-MS fragmentation pattern of [Co(tBu2DAD)2].

Figure S2 Schematic depiction of the reaction chamber of F-120 ALD reactor

Figure S3 Co3O4 film thickness vs distance from leading edge of the 5 x 5 cm2 silicon

substrate depending on the deposition temperature.

Figure S4 The photograph of Co3O4 thin film on Si and soda lime glass deposited at 120 °C

over 1000 cycles.

Figure S5 Plane view SEM of Co3O4 thin film deposited over 1000 cycles at 120 °C.

Figure S6 SEM image of Si trench with an aspect ratio of 20:1 (depth 40 m, width 2 m).

Figure S7X-ray Photoelectron Spectroscopy survey spectrum of Co3O4 thin films

Figure S8 UV-Vis transmission spectrum and corresponding Tauc plot of Co3O4 thin film


Figure S9 UV-Vis transmittance plots of a 100 nm TiO2 film (pristine TiO2) modified by the

depositing series of Co3O4 (10, 50, 100, 300, 500, and 10000 cycles) on the TiO2 films.

Figure S10 Photocurrent transients of TiO2/Co3O4 structures with depositing series of Co3O4

catalyst (10 – 1000 ALD cycles) on FTO glass under irradiation at different wavelengths (a),


122

selected area (b, c) and the corresponding photoaction spectra (d) measured in KOH (0.1 M)

at 1.48 V vs RHE at TiO2 and TiO2/Co3O4 photoanodes.

Figure S11 AFM image of Co3O4 deposited over 10 cycles at 120 °C on Si (100) substrate.

Figure S12 XPS spectra of Co3O4 thin films deposited over 10 cycles on Si and TiO2 at 120

°C.

Figure S13 XRD patterns of TiO2 deposited at 275 °C over 2000 cycles on FTO glass

Table S1 XPS surface distribution of Co, O, C, Ti and Si on samples deposited over 10 and 50 cycles

on a 100 nm thick TiO2 film and Si (100).


123

Figure S1 EI-MS fragmentation pattern of [Co(tBu2DAD)2].

The electron ionization mass spectrometry clearly identifies [Co(tBu2DAD)2] molecular ion

peak at m/z 395.3.

Figure S2 Schematic depiction of the reaction chamber of F-120 ALD reactor (cassette

configuration).


124

Figure S2. A schematic representation of the reaction chamber of the F-120 ALD reactor in

the “cassette configuration”. The dimensions of the schematic are not to scale.

Figure S3 Co3O4 film thickness vs distance from leading edge of the 5 x 5 cm2 silicon

substrate depending on the deposition temperature. All the samples were applied 300

deposition cycles.


125

Figure S4 The photograph of Co3O4 thin film on Si and soda lime glass deposited at 120 °C

over 300 cycles.

Co3O4 on Si (100) Co3O4 on soda lime glass Soda lime glass

Figure S5 Plane view SEM of Co3O4 thin film deposited over 1000 cycles at 120 °C.

500 nm 1.00 µm


126

Figure S6 SEM image of Si trench with an aspect ratio of 20:1 (depth 40 m, width 2 m).

Co3O4 film has been deposited over 1000 cycles at 120 °C using pulse lengths of 6 seconds

for both Co(tBu2DAD)2 and ozone. The purge length for both precursors was 10 seconds.

Thickness(nm) Top Middle Bottom

114 101 84

122 93 85

111 93 77

119 93 71

130 89 77

138 92 71

80

Average

thickness (nm) 122 94 78

Fully conformal Co3O4 films could not be deposited on 40 m Si trenches (aspect ratio of

1:20) despite using 6 s pulse and 10 s purge times of both precursors. A conceivable

explanation of for not achieving full conformality in the trench structure is the combined

effect of ozone decomposing effect of Co3O4 and high surface area of the substrate.


127

Figure S7 XPS survey spectrum of Co3O4 thin film deposited over 1000 cycles at 120 °C.

Figure S6 displays the XPS survey scan of Co3O4 that is dominated by cobalt and oxygen

photopeaks. No Ar+ sputtering experiment was performed.

Figure S8 UV-Vis transmission spectrum and corresponding Tauc plot of Co3O4 thin film



128

UV-Vis spectroscopy was performed on the as-deposited Co3O4 film grown on soda-lime

glass to determine the optical bandgap of Co3O4 thin films via Tauc plot. Obtained data

indicated a direct band gap value of 2.02 eV.

Figure S9 UV-Vis transmittance plots of a 100 nm TiO2 film (pristine TiO2) modified by the

depositing series of Co3O4 (10, 50, 100, 300, 500, and 10000 cycles) on the TiO2 films.


129

Figure S10 Photocurrent transients of TiO2/Co3O4 structures on FTO glass with varying

number of ALD cycles (10 – 1000) under irradiation at different wavelengths (a), selected

transients (b, c), and the corresponding photoaction spectra (d) measured in KOH (0.1 M) at

1.48 V vs RHE at TiO2 and TiO2/Co3O4 photoanodes.


130


131

Figure S11 AFM images of Co3O4 deposited over 10 cycles (a,b) and 50 cycles (c,d) at 120

°C on Si (100) substrate. After 10 deposition cycles, island-like nanoparticles are formed

instead of a closed film. After 50 deposition cycles, the island-like features are no longer

present and a homogeneous and smooth surface is observed, indicating that a closed film has

been formed. Images (a) and (b) were captured from different positions of a sample deposited

over 10 cycles. Images (c) and (d) were captured from different positions of a sample

deposited over 50 cycles.

Figure S12 XPS spectra of cobalt oxide deposited over 10 and 50 cycles on a 100 nm thick

TiO2 layer and on Si (100) substrate at 120 °C.


132


133

Table S1. XPS surface distribution of Co, O, C, Ti and Si on samples deposited over 10 and 50

cycles on a 100 nm thick TiO2 film and Si (100).

In samples deposited over 10 cycles on Si (100) and TiO2, the signal from the substrate is observed,

indicating that the formed cobalt oxide film is not closed, but island-like nanoparticles are formed

instead. After 50 deposition cycles on both Si (100) and TiO2, the signal from the substrate is no

longer observed, indicating that a closed layer has been formed.

Co % O %

Co O C Ti Si Total CoO Co(OH)2 Co3O4 O2- OH-

10 cycles on TiO2 4.82 44.38 41.38 9.43 0.00 100.01 24.90 52.28 22.82 51.17 48.83

50 cycles on TiO2 14.41 47.92 37.37 0.00 0.00 100.00 50.94 0.00 49.06 41.39 58.31

10 cycles on Si (100) 3.80 33.01 25.34 0.00 37.86 100.01 35.53 57.37 7.11 16.69 83.31

50 cycles on Si (100) 13.15 47.42 39.43 0.00 0.00 100.0 39.62 0.23 60.15 37.03 62.97


134

Figure S13 XRD patterns of TiO2 deposited at 275 °C over 2000 cycles on FTO glass

GI-XRD reflections of TiO2 films deposited at 275 °C on FTO show mixed phases of

anatase/rutile dominated by the anatase phase.1

References:


135

7.

Homoleptic all nitrogen coordinated bis-guanidinato

cobalt (II) complex: Volatile and thermally stable

precursors suitable for ALD/CVD


136

7. Homoleptic all nitrogen coordinated bis-guanidinato cobalt (II)

complex: Volatile and thermally stable precursors suitable for

ALD/CVD

7.1 Abstract

This work describes the synthesis of novel homoleptic all nitrogen coordinated bis-guanidinato

cobalt (II) complexes. The used guanidinato ligands feature different side groups attached to

the guanidinates, namely isopropyl and cycohexyl. Interestingly, after reaction of the ligand

precursors with the cobalt (II) source a carbodiimide insertion occurs in the case of the isopropyl

containing guanidinato ligands, which is not observed in the case of cyclohexyl. In this work

the chemistry of steric hindrance effect of cobalt guanidinate complexes will be discussed. The

cobalt (II) complexes were fully characterized using NMR spectroscopy, single crystal X-ray

diffraction and TGA-DSC.

7.2 Introduction

Highly conformal thin films of metal or metal oxides are highly desired for their applications

in worldwide field including microelectronics, optics, protection against corrosion and

oxidation, diffusion barriers, sensor for gas or liquid chemicals, photo sensitive coatings and so

on. Although chemical vapor deposition techniques including atomic layer depositions are

widely used to provide very uniform and conformal thin films, suitable and effective precursors

remained scarce. The criteria of ALD precursors are as follow. 1) Highly reactive towards the

functionalities on the surface as well as surface prepared by complementary reactant. 2) Volatile

and thermally stable at growth temperatures (> seconds) and sublimation temperatures (>

months). 3) Non-reactive and non-corrosive byproduct formation is preferred. Chronological


137

development of precursors including metal halides, Cps, alkoxides, b-ketonates, alkylamides,

TMS, heteroleptic compounds of mixture of theses ligands meet several limits. Metal halides

produce highly corrosive byproducts and precursors involving M¬C bonds lead to carbon

incorporation into the resulting films.2-3

Precursors containing metals for chemical vapor depositions were investigated across the across

the periodic table for the last century. While oxygen based precursors has reached the limit,

nitrogen based ligand system has caught an attention due to its ease of tunable steric bulk and

electronic saturation. In fact, the presence of two substituents (NR2) at the nitrogen atom readily

leads to increase of steric hinderance compared to oxygen based system (OR). Consequently, a

higher steric crowding surround the electro positive metal atom prevents the oligomerization

which influence the volatility of the compounds. Amidinates were intensively investigated

which diminish the drawbacks of conventional precursors.3 Our interest to develop reactive,

volatile and thermally stable all nitrogen coordinated cobalt complexes as CVD/ALD

precursors, we were inspired by the guanidinates as versatile ligand system closely related to

amidinates. Guanidinates have caught attention as ligand for transition metals, main group3-4

and lanthanides. Rare earth guanidinate are not so common still can be found in several

literatures.5

Guanidinates are in similarity of amidinates in terms of steric hinderance, however guanidinates

possess extended electronic flexibility where the lone pair electrons of the amido-nitrogen are

delocalized in the ligand -system.2 Additionally, guanidinate ligand is stronger base than the

amidinate which will prompt the reactivity of corresponding guanidinato metal complexes.

Synthetic strategy of guanidinato complex include several routes,2, 6 however we will focus on

salt metathesis approach in the paper.2, 7-8


138

We have synthesized homoleptic all nitrogen coordinated bis-guanidinato cobalt (II) complexes

with the general formula of [M((NR’)2CNR2)2]and the steric bulk effect to stabilize the bis-

guanidinato complexes depends on R’ substituent.


139


Synthetic strategy of guanidinato complex include several routes,6 however we will focus on

salt metathesis approach in this work.7-8 The salt metathesis contains two step reaction.

Stoichiometric reaction of a carbodiimide (CDI) with lithium amide generates a lithium

guanidinate [Li((NR’)2CNR2)]. An in-situ reaction with metal halide affords the desired

guanidinate complex along with LiCl as a byproduct.

Stoichiometric reaction of iPrCDI and LiNMe2 results in Li(iPr2Guan) (iPr2Guan =

(NiPr)2CNMe2). The reaction of two equivalents of Li(iPr2Guan) with CoCl2 was expected to

result in Co(iPr2Guan)2. Unexpectedly, heteroleptic compound [CoII((NiPr)2CNMe2)8

(NiPr)2CNMe2(iPrNHCNiPr))] (5) was obtained whereas iPrCDI insertion occurred on the

guanidinate ligand (Scheme 7.1 and Figure 7.1). In fact, homoleptic six-fold coordinated

guanidinate compounds (tris-guanidinates) are already known for second/third row transition

metals, metalloid such as antimony and rare earth metals. Meanwhile guanidinates (e.g. 2,6-

diisopropylphenyl, 2,4,6-mesityl) with high streric bulk ligands were used to stabilize the low

coordination first row transition metal (I) complexes9 but two guanidinates coordination

complexes were not investigated but still bis-guanidinate compounds are not investigated.

One molecule of iPrCDI cleaves the cobalt-N bond and lead to a wider N−M−N angel to stabilize

the compound 5. Interestingly, the structurally similar ligand system iPrAMD is known that it

leads to a homoleptic cobalt amidinate compound.10 This can be explained by the difference of

the electronic situation between the amidinates and guanidinates. Richer electron density and

electronical flexibility on the iPrguan ligand discourage the iPr substituent to be not bulky

enough for stabilization of the Co(II) metal center. On the other hand, our attempt of

reproducing Co(iPrAMD)2 afforded contrasting results.10 According to our observation,


140

dimerization occurred on Co(iPrAMD)2 to yield [Co(iPrAMD)2]2 (7) which has been observed

for the Fe and Mn amidinates with iPr-MeAMD ligand.10 (Scheme 7.1 and Figure 7.3) The

resulting compounds 5 and 7 suggest that it is challenging for the iPr group to stabilize the

cobalt bis- amidinates/guanidinates complexes.

Reaction with employing cyclohexyl group instead of iPr in a similar fashion as compound 5

led to homoleptic bis-guanidinate complex, [Co((CyN)2CN(CH3)2)2] that the steric hindrance

from dialkylcarbodiimide has increased. (Scheme 7.1)

Scheme 7.1 Synthetic scheme of guanidinates according to the steric hinderance.

The solid state molecular structures of [CoII((NiPr)2CNMe2)((NiPr)2CNMe2(iPrNHCNiPr))] (5)

and [Co(Cyguan)2] (6) determined by single crystal X-ray diffraction analysis. The crystal

system of compounds 5 and 6 were monoclinic (space group P2/1c) and triclinic (space group


141

P-1). Crystallographic refinement data of the compounds 5-7 can be found section in 7.5.3. All

the Co−N bond lengths of heteroleptic compound 5 show in the same range (2.022 Å). The

bond angle of N4−Co−N5 from the ligand where the CDI insertion took place displays much

wider angle (96.16(12) °) than N1−Co−N2 in the guanidinate ligand (65.97(12) °). (Figure 7.1

and Table 7.1) Predictably, in compound 6 the bond lengths of Co−N and the angles of

N−Co−N are in the same range (2.016 Å and 66.62 °) Both structures show more or less strong

distortion of tetrahedron geometry, however the distortion observed in 6 was more prominent

than in 5. This is ascribed to the cyclohexyl group which is much higher sterically demanding

compared to iso-propyl group, enables the nitrogen atoms from each guanidinates ligands are

more distanced. (Figure 7.2 and Table 7.2)

The solid state X-ray crystal structure of [Co(iPrAMD)2]2 (7) shows the dimerized structure

which has not been reported where only the monomeric Co(iPrAMD)2 is reported. [Gordon] We

postulate the both monomeric and dimeric structures are in the equilibrium in the solution so

that the crystallization behavior can differ dependent on the applied crystallization condition.

The structure of dimeric compound 7 is shown in Figure 7.3, and selected bond distances and

angles are contained in Table 7.3. Crystallographic data can be found in Table 7.4 in section

7.5.3. Each cobalt atoms in dimeric compound 7 are bridged by two 1-amidinate ligands and

one chelated by one 2-amidinate ligand. The Co−N bond lengths of (2.0880(12)-2.0731(12)

Å) in the terminal chelating ligands are slightly enlongated than the Co−N distances in the

bridging ligand (2.0450(12)-2.430(12) Å), but are in the same range. The compound 7 is not of

direct goal and interest in this work, further characterization of 7 was not performed.


142

Figure 7.1 Povray plot of the molecular structure of compound 5 in the solid state as

determined by single crystal X-ray diffraction. Thermal ellipsoids are shown at the 50 %

probability level and the hydrogen atoms are omitted for clarity.

Table 7.1 Selected Bond Length (Å) and Angles (°) for

[CoII((NiPr)2CNMe2)((NiPr)2CNMe2(iPrNHCNiPr))] (5)

Co−N(1) 2.074(3) N(1)−Co−N(2) 65.97(12)

Co−N(2) 2.017(3) N(4)−Co−N(5) 96.16(12)

Co−N(4) 1.969(3) N(1)−Co−N(5) 115.87(12)

Co−N(5) 2.029(3) N(2)−Co−N(4) 128.34(13)

N(1)−C(1) 1.328(5) Co−N(4)−C(10) 110.6(2)

N(2)−C(1) 1.340(5) Co−N(5)−C(20) 116.3(2)

N(4)−C(10) 1.360(5) N(4)−C(10)−N(6) 112.2(3)

N(5)−C(20) 1.316(5) N(5)−C(20)−N(6) 119.5(3)

N(6)−C(10) 1.478(5) C(10)−N(6)−C(20) 119.3(3)

N(6)−C(20) 1.376(5)


143

N(7)−C(10) 1.267(5)

Figure 7.2 Povray plot of the molecular structure of [Co(Cyguan)2] (6) (one of the two whole

fragments in the asymmetric unit are shown) in the solid state as determined by single crystal

X-ray diffraction. Thermal ellipsoids are shown at the 50 % probability level and the

hydrogen atoms are omitted for clarity. Structural disorder is confined to the cyclohexyl

groups in the other half of fragments.

Table 7.2 Selected Bond Length (Å) and Angles (°) for [Co(CyGuan)2] (6)

Co−N(1) 2.023(3) N(1)−Co−N(2) 66.53(13)

Co−N(2) 2.012(3) N(4)−Co−N(5) 66.70(13)

Co−N(4) 2.009(3) N(1)−Co−N(4) 129.77(14)

Co−N(5) 2.021(3) N(2)−Co−N(5) 132.40(14)

N(1)−C(1) 1.336(5)

N(2)−C(1) 1.345(5)

N(4)−C(16) 1.348(5)

N(5)−C(16) 1.348(5)


144

N(3)−C(1) 1.374(5)

N(6)−C(16) 1.363(5)

Figure 7.3 Molecular structure (POV-ray plot) of [Co(iPrAMD)2]2 as determined by single-

crystal X-ray diffraction. Displacement ellipsoids are shown at the 50% probability level, and

hydrogen atoms are omitted for clarity.

Table 7.3 Selected Bond Length (Å) and Angles (°) for [Co(iPrAMD)2]2 (7)

Co−N(1) 2.0880(12) N(1)−Co−N(2) 64.50(5)

Co−N(2) 2.0731(12) N(3)−Co−N(4) 132.45(5) Co−N(3) 2.0450(12) N(1)−Co−N(3) 113.42(5)

Co−N(4) 2.0430(12) N(1)−Co−N(4) 106.97(5)

N(1)−C(1) 1.333(2) N(2)−Co−N(3) 105.80(5) N(2)−C(1) 1.325(2) N(2)−Co−N(4) 113.70(5)

N(3)−C(9) 1.329(2) N−C−Nchelating 113.28(13)

N(4)−C(9) 1.332 N−C−Nbridging 116.01(13)


145

A crude oil of compound 5 as synthesized without crystallization was measured TGA to study

thermal behavior. (Figure 7.4) TGA curve shows onset of volatilization (1 % weight loss) at

73 °C and a shouldered curve can be seen at ca. 220 °C that is a phenomenon named CDI

deinsertion of guanidinate demonstrated in previous report.11 The final residual mass show ca.

10 %. Isothermal studies at ambient pressure exhibit non-linear weight loss which is attributed

to a partial decomposition of ligand (CDI deinsertion from ((NiPr)2CNMe2(iPrNHCNiPr))).

TGA studies were repeated on crystallized compound 5 in combination with DSC (Differential

Scanning Calorimetry) to screen the solid-liquid phase transition. (Figure 7.5) In the solid state

TGA, a single step weight loss was observed due to the higher purity and less contact to air

during the sample loading. The compound 5 is in the liquid state at room temperature and

crystallizes at ca. -30 °C. Notably, it is observed that after warming up the crystals to room

temperature, the compound remains in the solid state. DSC studies confirm this behavior. After

cooling, a phase transition is observed in the DSC trace, however, on the heating branch the

phase transition to solid occurs at substantially higher temperature (75 °C). This result indicates

a good agreement with the melting point found in DTA. Both measurements TGA/DTA and

DSC were using a heating rate of 5 K/min which was apparently insufficient to trigger the phase

transition in the used temperature range.


146

Figure 7.4 Thermal properties of compound 5 as crude oil, TGA/DTA (left) and isothermal

TG studies (right).

Figure 7.5 Thermal properties of compound 5 as crystal pellets (left) and DSC studies (right).


147

TGA studies of 6 at ambient pressure displays onset of volatilization at 104 °C and a shouldered

curve can be seen at 180 °C which is caused by aforementioned CDI deinsertion.11 The residual

weight was found approximately 10 %. (Figure 7.6) Isothermal studies at ambient pressure at

90 °C showed linear weight loss whereas at 100 °C exhibited relatively non-linear behavior.

The evaporation rates as calculated from the slope of the isothermal TGA curves at 90 and 100

C were 3.67 mg/min and 6.95 mg/min. The isothermal studies at 90 °C indicate capability of

sustainable transport of precursor during the deposition time (180 min).

Figure 7.6 Thermal properties of compound 6 as crude oil, TGA/DTA (left) and isothermal

TG studies (right).


148

Figure 7.7 Thermal properties of compound 5 as crystal pellets (left) and DSC studies (right).

7.4 Conclusion

Within this chapter the synthesis of a new cobalt-guanidinate precursor, namely [Co(CyGuan)2]

is discussed. We found an astonishing dependence of the bonding situation at the final precursor

and the R-groups on the used guanidinates. In the case of small iPr groups, a CDI-insertion

occurs, leading to the formation of a heteroleptic complex. When a much bulkier R-group is

used in the preparation of the precursor, for instance cyclohexyl, a homoleptic guanidinate

complex is achieved. This insertion has a dramatic effect on the thermal properties and the

volatilization of the compound, increasing the temperature when the compound enters the gas

phase. We showed that the use of different R-groups is controlling the insertion, which weakens

the usability of the compounds as precursors. By employing bulky side groups, it was possible

to prevent the insertion effect and to obtain the homoleptic cobalt guanidinate compounds.

It is planned in future studies to analyze the preparation of cobalt oxide thin films using ALD

and CVD methods. We expect to be able to utilize this precursor in the development of a

systematic deposition study towards the before mentioned materials. Further studies include

the alteration of the R-groups on the guanidinates in order to understand their influence on the


149

inclusion reaction and to demonstrate the tunability of this class of ligands by slight alterations

on the ligand backbone.


150



Material and Methods. All manipulations were carried out in an atmosphere of purified argon

using standard Schlenk and glove-box techniques. n-Hexane, n-pentane, toluene, diethylether

were dried using an MBraun Solvent Purification System. Tetrahydrofuran and d6-benzene

were dried by passing through a column of dried activated neutral Al2O3. The final H2O content

in all solvents was checked by Karl Fischer titration and did not exceed 5 ppm. All

characterization and instrumental details are identical described in chapter 3.6 and 6.5. Lithium

guanidinate species, [Li(NR)2CNMe2] were prepared by stoichiometric reaction of LiNMe2 and

corresponding dialkylcarbodiimide in diethylether in prior to the salt metathesis reaction and

used without any further isolation or purification.

7.5.2 Synthetic Procedure

[CoII((NiPr)2CNMe2)((NiPr)2CNMe2(

iPrNHCNiPr))] (5) Freshly prepared [Li(iPr)2CNMe2]

etherate solution was added into a CoCl2 (0.5 equivalent) etherate solution at 0 °C. The reaction

mixture was stirred overnight at room temperature. All the volatiles were removed under

vacuum and the residue was extracted with n-hexane. The residual solution was filtered through

the celite pad in a shlenk frit to remove LiCl salts. The filterate was concentrated to a quarter

of initial volume, then recrystallized at -30 °C. Blue crystals suitable for single crystal X-ray

diffraction were obtained.


151

[Co(CyGuan)2] (6) Freshly prepared [Li(Cy)2CNMe2] etherate solution was added into a CoCl2

(0.5 equivalent) etherate solution at 0 °C. The reaction mixture was stirred overnight at room

temperature. All the volatiles were removed under vacuum and the residue was extracted with

n-hexane. The residual solution was filtered through the celite pad in a shlenk frit to remove

LiCl salts. The filterate was concentrated to a quarter of initial volume, then recrystallized at -

30 °C. Blue-violate crystals suitable for single crystal X-ray diffraction were obtained.

[Co(iPrAMD)2]2 (7) was prepared by a modified procedure described in the literature.10 A

solution of methyllithium (1.6 M in Et2O) was added dropwise to a etherate solution of 1,3-

diisopropylcarbodiimide in 1:1 molar ratio at -30 °C. The reaction mixture was stirred for

overnight at room temperature. The formed Li(iPrAMD) solution was added into an Et2O

solution of CoCl2 (0.5 equivalent) by means of cannula at 0 °C. The reaction mixture was stirred

overnight at room temperature. All the volatiles were removed under vacuum and the residue

was extracted with n-hexane. The extract was filtered through a celite pad on a schlenk frit to

afford dark blue solution. The filtrate was concentrated to 10-15 mL and recrystallized at -30 °C.


152

7.5.3 Crystallographic data

Table 7.4 Crystallographic Data Crystallographic data and refinement details of compounds 5-7.

5 6 7

Chemical formula C25H55CoN8 C30H68Co1N6

(C60H116Co2N12) C32H68Co2N8

Formula weight 526.70 561.75 (1123.50) 682.80

Crystal system monoclinic triclinic monoclinic

Space group P21/c P-1 C2/c

a (Å) 20.1386(3) 10.5285(3) 23.1963(4)

b (Å) 9.42059(14) 16.0905(6) 9.5810(2)

c (Å) 16.3758(3) 19.0321(6) 18.0658(3)

(°) 100.9386(19) 96.101(2) 110.788(2)

Volume (Å3) 3050.33(9) 3159.69(17) 3753.63(13)

Z 4 2 4

Dcalc (g × cm-3) 1.147 1.181 1.208

Absorption coefficient (mm-1) 4.599 4.453 7.151

F(000) 1152.0 1228.0 1480.0

2θ range for data collection (°) 8.944 to 152.716 6.864 to 153.088 8.154 to 152.774

Reflections collected/unique 25068/6271 [Rint =

0.0548]

57520/13133 [Rint =

0.1086]

19281/3903 [Rint =

0.0315]

Data/restraints/parameters 6271/0/324 13133/0/675 3903/0/200

goodness-of-fit on F2 1.213 1.029 1.050

Final R indices [I > 2(I)] R1 = 0.0566, wR2 =

0.1447

R1 = 0.0670, wR2 =

0.1627

R1 = 0.0281, wR2 =

0.0703

R indices (all data) R1 = 0.0726, wR2 =

0.1503

R1 = 0.0897, wR2 =

0.1752

R1 = 0.0331, wR2 =

0.0727


153

8. References

1. Ballirano, P.; Caminiti, R., Rietveld refinements on laboratory energy dispersive X-ray

diffraction (EDXD) data. J. Appl. Crystallogr. 2001, 34, 757-762.

2. Bailey, P. J.; Pace, S., The coordination chemistry of guanidines and guanidinates.

Coord. Chem. Rev. 2001, 214, 91-141.



4. Coyle, J. P.; Johnson, P. A.; DiLabio, G. A.; Barry, S. T.; Müller, J., Gas-Phase

Thermolysis of a Guanidinate Precursor of Copper Studied by Matrix Isolation, Time-of-Flight

Mass Spectrometry, and Computational Chemistry. Inorg. Chem. 2010, 49, 2844-2850.

5. Milanov, A. P. MOCVD and ALD of Rare Earth Containing Multifunctional Materials:

From Precursor Chemistry to Thin Film Deposition and Application. Dissertation, Ruhr-

University Bochum, Bochum, Germany, 2010.

6. Musashi, Y.; Sakaki, S., Insertion of carbon dioxide into a rhodium(III)-hydride bond:

a theoretical study [dagger]. Journal of the Chemical Society, Dalton Transactions 1998, 577-

584.

7. Edelmann, F. T., Chapter 3 - Advances in the Coordination Chemistry of Amidinate and

Guanidinate Ligands. In Adv. Organomet. Chem., Anthony, F. H.; Mark, J. F., Eds. Academic

Press: 2008; Vol. Volume 57, pp 183-352.

8. Edelmann, F. T., Lanthanide amidinates and guanidinates: from laboratory curiosities

to efficient homogeneous catalysts and precursors for rare-earth oxide thin films. Chem. Soc.

Rev. 2009, 38, 2253-2268.

9. Jones, C.; Schulten, C.; Rose, R. P.; Stasch, A.; Aldridge, S.; Woodul, W. D.; Murray,

K. S.; Moubaraki, B.; Brynda, M.; La Macchia, G.; Gagliardi, L., Amidinato– and Guanidinato–


154

Cobalt(I) Complexes: Characterization of Exceptionally Short Co–Co Interactions. Angew.

Chem., Int. Ed. 2009, 48, 7406-7410.



7951-7958.

11. Kenney, A. P.; Yap, G. P. A.; Richeson, D. S.; Barry, S. T., The Insertion of

Carbodiimides into Al and Ga Amido Linkages. Guanidinates and Mixed Amido Guanidinates

of Aluminum and Gallium. Inorg. Chem. 2005, 44, 2926-2933.

Curriculum Vitae

155

Curriculum Vitae

Jiyeon Kim

E-mail: [email protected]

PROFESSIONAL EXPERIENCE

1/2017 6/2017 Scientific Researcher Technical University Munich, Chair of Inorganic and Metal Organic

Chemistry

Synthesis of Rhenium Sulfide nanoparticles for anti-skin cancer application

12/2012 – 12/2016 Scientific Researcher Ruhr-University Bochum, Chair of Inorganic Chemistry II

Atomic Layer Deposition (ALD) of Transition Metal Oxides Thin Film and Precursor Chemistry

Synthesis of Organometallic Complexes Expertized in Handling Extremely Air Sensitive Materials

Analytic Techniques; Single Crystal X-ray Diffraction, TG, XRD, XPS, AFM, SEM, NMR, IR, EI-MS etc.

ALD Process Development

Teaching Assistant in Advanced Inorganic Chemistry (Lab Course, 4 semesters in total) and Supervision of Bachelor and Master Students

09/2012 – 11/2012 Research Assistant Kookmin University, Laboratory of Inorganic Chemistry

Synthesis of Metal/Metal Oxide Nanoparticles and Their Surface Modification via Ligand Exchange

03/2012 – 05/2012 Visiting Researcher Ruhr-University Bochum, Chair of Inorganic Chemistry II

Metal Organic Framework coated Silver Nanowires

03/2010 – 02/2012 Research Assistant

Kookmin University, Laboratory of Inorganic Chemistry

Photo-luminescent Ceramic Nano Materials

Analysis of Fluorescent Materials (NMR, UV-Vis, PL)

01/2009 – 02/2010 Undergraduate Research Opportunities Program (UROP)

Kookmin University, LABORATORY of Inorganic Chemistry

mailto:[email protected]

Curriculum Vitae

156

EDUCATION

12/2012 – 4/2017 Doctor of Philosophy (Ph.D.) Inorganic Chemistry Bochum, Germany Chair of Inorganic Chemistry II, Ruhr-University Bochum

Prof. Dr. Anjana Devi and Prof. Dr. Roland A. Fischer

“Precursor Chemistry for Atomic Layer Deposition of Metal Oxides”

Development of novel cobalt precursor for ALD and process aiming

for photoelectrocatalytic water splitting application.

“Synthesis of Heteronuclear Metal Complexes Containing Direct Metal-Metal Bonds” Metal-Metal bond formation via Reductive Elimination

03/2010 – 02/2012 Mater of Science (M.Sc.) Chemistry

Seoul, Republic of Korea Inorganic Chemistry, Kookmin University, Prof. Dr. Sungho Yoon GPA 4.36 / 4.5

“Surface Modification of Silica Nanoparticles with Zn(II) Complexes Mimicking the Active Site of Carbonic Anhydrase”

03/2006 – 02/2010 Bachelor of Science (B.Sc.) Chemistry Seoul, Republic of Korea Inorganic Chemistry, Kookmin University, Prof. Dr. Sungho Yoon

GPA 3.26 / 4.5

“Investigating the Gelation Properties of Mixed Ag(I) Carboxylates”

INTERNATIONAL EXPERIENCE

03/2016 and 06/2015 Research Stay Helsinki, Finland University of Helsinki, Helsinki, Finland

Prof. Dr. Markku Leskelä “Atomic Layer Deposition of Cobalt Oxide”

Development of Ozone Assisted ALD Process Resulting in Co3O4 Thin Films for Photoelectrocatalysis

01/2013 – 12/2015 Research Contribution 4G-Photocat EU Project (FP7-309636) Objectives: Development of Highly Active Composite Photocatalysts Based on Cheap and Abundant Elements, and Their Deposition onto Various Surfaces.

Lab Visits for Scientific Presentation and Discussion during the Project in Czech Republic, Finland, Vietnam, Poland, Malaysia

07/2014 Research Visit Sapporo, Japan Hokkaido University, Sapporo, Japan

Prof. Dr. Hajime Ito Organometallic Chemistry and Catalysis (C-H Activation)

Curriculum Vitae

157

FELLOWSHIPS & HONOURS

05/2013 – 12/2015 4G-Photocat EU Project Ph.D. Fellowship

07/2014 – 07/2016 Two Ruhr-University Bochum Research School Plus Grants for

International Projects

02/2012 Excellent Researcher Scholarship from Kookmin University

LANGUAGE SKILLS

Korean Native English Fluent in Spoken and Written Form

2.5 Years Elementary School in USA (Los Angeles County, CA) TOFEL Score of 91 in 2012 Official Language during Ph.D. Project

German Basic in Spoken and Written Form

SOFTWARE SKILLS

Microsoft Office (Word, Power Point, Excel), Origin

Photoshop, CorelDraw, ChemDraw, POV-Ray

Shelxl, Olex

Jiyeon Kim July, 20th, 2017

Curriculum Vitae

158

PUBLICATIONS

Homoleptic all nitrogen coordinated bis-guanidinato cobalt (II) complex: Volatile and

thermally stable precursor suitable for ALD/CVD Jiyeon Kim, Niklas Stegmann, Stefan Cwik and Anjana Devi*

Manuscript in progress 2017

Low temperature atomic layer deposition of cobalt oxide as an effective catalyst layer for

photoelectrochemical water splitting devices Jiyeon Kim, Tomi Iivonen, Jani Hämäläinen, Marianna Kemell, Kristoffer Meinander,

Kenichiro Mizohata, Radim Beranek, Markku Leskelä and Anjana Devi*

Accepted in Chemistry of Materials (ACS) 2017 (DOI: 10.1021/acs.chemmater.6b05346)

Oxidation of Nickel-ECp* Complexes: Stable Open-Shell NiI Cations [Ni(ECp*)n(PPh3)4-n]+ (n =

2, 4; E = Al, Ga) Jiyeon Kim, Markus Halbherr, Christian Gemel and Roland A. Fischer*

Inorganic Chemistry, 2015, 54, 9675

Comparative Synthesis of Cu and Cu2O Nanoparticles from Different Copper Precursors in an

Ionic Liquid or Propylene Carbonate Raquel Marcos Esteban, Hajo Meyer, Jiyeon Kim, Christian Gemel, Roland A. Fischer* and Christoph

Janiak*

Eur. J. Inorg. Chem. 2016, 2016, 2106

Low-temperature atomic layer deposition of copper(II) oxide thin films Tomi Iivonen*, Jani Hämäläinen, Benoît Marchand, Kenichiro Mizohata, Miika Mattinen, Georgi Popov,

Jiyeon Kim, Roland A. Fischer, and Markku Leskelä Journal of Vacuum Science & Technology A, 2016, 34, 01A109

A fluorescent ammonia sensor based on a porphyrin cobalt(II)–dansyl complex Jiyeon Kim, Si Hyung Lim, Yeoil Yoon, T. Daniel Thangadurai and Sungho Yoon*

Tetrahedron Letters, 2011, 52, 2645

CONFERENCE

7/2016 Low Temperature Ozone Assisted ALD of Co3O4

Dublin, Ireland Jiyeon Kim, Tomi Iivonen, Radim Beranek, Markku Leskelä and Anjana Devi Oral 16th Atomic Layer Deposition Conference, Dublin, Ireland

8/2015 Low Valent Group 13 Organyls at Transition Metals

Boston, USA Jiyeon Kim, Christian Gemel and Roland A. Fischer Oral + Poster

Precursor Synthesis and Atomic Layer Deposition of CoOx Thin Films Jiyeon Kim, Tomi Iivonen, Roland A. Fischer, Markku Leskelä and Anjana Devi

250th National Meeting of the American Chemical Society

7/2014 Transition Metal-mediated Elimination of H2 from (Organo-)Al Hydrides

Sapporo, Japan Jiyeon Kim, Christian Gemel and Roland A. Fischer Poster XXVI International Conference on Organometallic Chemistry

Oral The Coordination Chemistry of Low Valent Group 13 Species at Transition

Metal Complexes Jiyeon Kim, Christian Gemel and Roland A. Fischer

International Workshop of the Japanese Society of Coordination Chemistry

Curriculum Vitae

159

Documents

Organometallic chemistry of transition metal - group 13