Synthesis, Characterization and Structural Analysis of ... thesis_FINAL.pdf · Figure 6.6 1H-NMR 4-(nicotinamido)benzoic acid (L1B2) in DMSO-d6 29 Figure 6.7 1H-NMR 4-(nicotinamido)

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Synthesis, Characterization and Structural Analysis of Supramolecular Metallogels

Alfreð Aðalsteinsson

Faculty of Physical Sciences University of Iceland

2017

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Synthesis, characterisation and structural analysis of supramolecular metallogels


15 ECTS thesis submitted in partial fulfilment of Baccalaureus Scientiarum degree in Chemistry

Advisor Dr. Krishna Kumar Damodaran

Faculty of Physical Sciences School of Engineering and Natural Sciences

University of Iceland Reykjavík, May 2017

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Synthesis, Characterization and Structural Analysis of Supramolecular Metallogels Efnasmíð, greining og könnun á þversameinda málmgelum 15 ECTS thesis submitted in partial fulfillment of a B.Sc. degree in Chemistry Copyright © 2017 Alfreð Aðalsteinsson All rights reserved Faculty of Physical sciences School of Engineering and Natural Sciences University of Iceland VRII, Hjarðarhaga 2-6 107 Reykjavík Iceland Telephone: 525 4700 Bibliographic information: Alfreð Aðalsteinsson, 2017, Synthesis, Characterisation and Structural Analysis of Supramolecular Metallogels, B.Sc. thesis, Faculty of Physical Sciences, University of Iceland, 52 pp. Printing: Háskólaprent, Fálkagötu 2, 207 Reykjavík Reykjavík, May 2017

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Declaration of authorship I hereby declare that this report is written by me, is based on my own observations and has

not been previously submitted at part or in whole for a higher education degree.

Hér með lýsi ég því yfir að ritgerð þessi er samin af mér og að hún hefure hvorki að hluta

né í heild verið áður lögð fram til hærri prófgráðu.

_______________________________


220893-2519

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Abstract Supramolecular gels which involve low molecular weight gelators (LMWGs) have emerged as an abounding area of research in recent years due to their potential applications as functional soft materials for separation, contact lenses, drug delivery, arrangement of inorganic and polymer materials and as media to control crystal growth. Recently, there has been a boom of interest in metal-based supramolecular gels (metallogels), where metals have strong coordination interactions between the organic component, which are the main ingredients in the formation of a gel fibre network in combination with the assorted non-covalent interactions. The fibres of the gels themselves can occur from the self-assembly of various coordination polymers, metal complexes or even cross-linked coordination polymers. The understanding of how the structure of LMWGs and metallogels are understood in the gel state is still in its outset because of the low ordering of the gel as a whole and the wide range of length scale of the gel structure, which can range from nano- to microscale. In this project, a synthesis and characterization will take place of supramolecular gels based on metalloligands and if successful, an attempt to determine the gel structure will take place. This can be acheived by correlating the fibrous network network with SEM (scanning electron microscope) imaging, and for the crystal structure of the gelator with the X-ray diffraction pattern of the dried gel (xerogel).

Útdráttur Rannsóknir a þversameindagelum hafa aukist gríðarlega upp á síðkastið. Þessar auknu vinsældir má rekja til þeirra ótal möguleika sem þetta rannsóknarsvið hefur upp á að bjóða. Eins og notagildi þeirra til að aðskilja efni, augnlinsur, lyfjagjafir og myndun fjölliða sem miðill til þess að stjórna kristallsvexti. Þessi gel myndast þegar leysasameindirnar raðast upp í einskonar súlur eða keðjur, sem svo mynda þrívíða trefjakerfi. Þessi trefjakerfi samanstanda af reglulegri uppröðun sameinda í gegnum ósamgild tengi, eins og vetnistengi, π-π stöflun, van der Waals krafta, halógenatengi o.s.frv. Að undanförnu hefur verið mikill uppgangur á sviði málm-þversameindagelum, t.a.m málmgelum. Gel sem innihalda málma hafa sterka tilhneigingu til að tengjast lífræna- og málmhlutanum, sem eru helstu uppistöðurnar til að mynda gel. Trefjarnir af gelunum myndast þegar regluleg uppröðun á allskyns samhæfðum fjölliðum, málmkomplexum eða cross-linked fjölliðum á sér stað. Hvernig málmgel eru uppbyggð er að mestu óþekkt, þar sem „gelstrúktúrinn“ getur verið á breiðu lengdarbili, allt frá nanó- upp í míkróskala. Í þessu verkefni voru þversameindagel sem samanstanda af málmtenglum smíðuð og greind.

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Table of contents List of Schemes .................................................................................................................. vii

List of Figures ................................................................................................................... viii

List of tables ........................................................................................................................ ix

List of Abbreviations ........................................................................................................... x

Acknowledgements ............................................................................................................. xi

1 Introduction ...................................................................................................................... 1

1.1 Understanding metallogels architecture ............................................................................... 2 1.2 Amide based gelators and metallogels .................................................................................. 4

2 Aim and objective ............................................................................................................. 6

2.1 Strategy .................................................................................................................................... 6 2.2 Importance of functional groups ........................................................................................... 7

3 Experimental ..................................................................................................................... 8

3.1 Material and methods ............................................................................................................. 8 3.2 Synthesis of L1 ......................................................................................................................... 8

We have tried various methods to synthesise L1. First method was to protect the carboxylic

acid group by converting it to isopropyl ester (Figure 3.1) The detailed procedure are given

below. .......................................................................................................................................... 8 3.2.1 Synthesis of isopropyl 4-aminobenzoate and isopropyl 3-aminobenzoate ........................ 9 3.2.2 Synthesis of nicotinoyl and isonicotinoyl chloride ............................................................ 9 3.2.3 Synthesis of isopropyl 3- & 4-(nicotinamido)benzoate and isopropyl 3- & 4-

(isonicotinamido)benzoate .......................................................................................................... 9 3.2.4 Synthesis of L1 and L4 .................................................................................................... 10 3.2.5 Different approach to synthesize L1 ................................................................................ 10

3.3 Synthesis of L2 ....................................................................................................................... 12 3.4 Synthesis of metal complexes with L1 ................................................................................. 13

4 Results and discussion .................................................................................................... 14

4.1 Synthesis ................................................................................................................................. 14 4.1.1 Synthesis of amino benzoic acid esters ........................................................................... 14

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4.1.2 Synthesis of acid chloride ................................................................................................ 14 4.1.3 Synthesis of L1-L4 .......................................................................................................... 15

4.4 Gelation studies of L1 with various metals ......................................................................... 16 4.4 Tgel experiment on CuCl2 gel (L1B4) ................................................................................... 19 4.5 Gelation studies of L2 ........................................................................................................... 19 4.6 Metal complexes with L1B1 ................................................................................................. 19 4.7 SEM images of xerogels ........................................................................................................ 20

5 Conclusions ..................................................................................................................... 21

References .......................................................................................................................... 22

6 Supplementary information .......................................................................................... 24

6.1 1H-NMR of compounds in experimental section 3.1.1 – 3.1.4 ........................................... 24 6.2 1H-NMR of compounds in experimental section 3.2 .......................................................... 28 6.3 1H-NMR of L2B1 in experimental section 3.3 .................................................................... 32 6.4 13C-NMR of L1B4 .................................................................................................................. 33 6.5 Mass spectroscopy ................................................................................................................ 34 6.6 Gelation studies with 4-(nicotinamido)benzoic acid (L1B2) ............................................ 39 6.7 Gelation studies with 4-(nicotinamido)benzoic acid (L1B3) ............................................ 40

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List of Schemes Scheme 1.1 Description of how supramolecular gels are formed 1

Scheme 1.2 Incorporation of a metal, which coordinates to the pyridyl nitrogen 4

Scheme 2.1 Reaction scheme of the synthesis of the organic ligands 6

Scheme 3.1 Step-by-step scheme of protecting and deprotecting of acid group 8

Scheme 3.2 Reaction scheme, which shows the formation of L1 10

Scheme 4.1 Mechanism of esterification of amino benzoic acid with thionyl chloride 14

Scheme 4.2 Mechanism of the iso/nicotinic acid chloride 15

Scheme 4.3 Mechanism of the formation of L1 to L4 15

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List of Figures Figure 1.1 SEM images, which display fibrous network 2

Figure 1.2 Explains the structure of a) primary, b) secondary and c) tertiary structures of urea based supramolecular gel 3

Figure 1.3 a) Bidentate and monodentate hydrogen-bonding of urea. b) monodentate hydrogen-bonding of amide 5

Figure 4.1 Gels that passed the inversion test 18

Figure 4.2 SEM images of M:L ratio 1:1 gels in DMSO/H2O 20

Figure 6.1 1H-NMR of isopropyl 4-aminobenzoate in CDCl3 24

Figure 6.2 1H-NMR of isopropyl 3-aminobenzoate in CDCl3 25

Figure 6.3 1H-NMR of isopropyl 4-(nicotinamido)benzoate in CDCl3 26

Figure 6.4 1H-NMR of isopropyl 4-(isonicotinamido)benzoate in CDCl3 27

Figure 6.5 1H-NMR of 4-(nicotinamido)benzoic acid (L1B1) in DMSO-d6 28

Figure 6.6 1H-NMR 4-(nicotinamido)benzoic acid (L1B2) in DMSO-d6 29




Figure 6.10 13C-NMR of 4-(nicotinamido)benzoic acid (L1B4) in DMSO-d6 33

Figure 6.11 MS of 4-(nicotinamido)benzoic acid (L1B1) in methanol 34





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List of tables Table 3.1 Yields from the succesfully synthesized ligands (L1 and L2) 12

Table 4.1 Gelation studies of L1B1 with different metal salts 16

Table 4.2 Gelation studies of L1B1 to find minimum wt% 17

Table 4.3 Gelation studies of L1B4 with various metal salts 18

Table 4.4 Tgel experiments with 2.4 wt% CuCl2 metallogels 19

Table 4.5 Synthesis of metal complexes (crystals) with L1B1 20

Table 6.1 Gelation studies of L1B2 39



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List of Abbreviations LMWG Low molecular wieght gelators

3-D Three dimensional

2-D Two-dimensional

DMSO Dimethyl sulfoxide

DMF N,N-Dimethylformamide

THF Tetrahydrofuran

DCM Dichloromethane

CHCl3 Chloroform

SAFIN Self-assembled fibril network

Wt% Weight percentage

Tgel Temperature at which gel becomes soltion (gel-sol temperature)

L1 4-(nicotinamido)benzoic acid

L2 3-(nicotinamido)benzoic acid

L3 3-(isonicotinamido)benzoic acid

L4 4-(isonicotinamido)benzoic acid

4PNA 4-(pyridyl)nicotinamide

MS Mass spectroscopy

NMR Nuclear magnetic resonance

δ Chemical shift

s Singlet

d doublet

t triplet

dd doublet of doublets

dt doublet of triplets

SEM Scanning electron microscope

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Acknowledgements I would like to give my special thanks to my supervisor Dr. Krishna K. Damodaran for his

guidance and support. I also thank my associates in the laboratory, especially Dipankar

Ghosh for his patience and assistance.

I would also like to thank Dr. Sigríður Jónsdóttir for carrying out the spectroscopic

measurements.

Furthermore, I would like to thank Prof. Kesara Anamthawat-Jónsson for her effort and

time she put into assisting me with the SEM imaging.

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1 Introduction Supramolecular gels based on low molecular weight gelators (LMWGs) are generally

formed by the immobilisation of the solvent molecules in the 3-D network of the

molecules, which are directionally dependent 3D structures in solution. The practical

uses of these gels have been in drug delivery, contact lenses, shaving creams and etc.

Supramolecular gels can be formed via weak non-covalent interactions such as van der

Waals, hydrogen bonding, π-π, and ionic interactions. Supramolecular gels can be

categorized into hydrogels and organogels. Hydrogels are the type of gels that

immobilize water and organogels immobilize organic solvents. However it’s possible to

make supramolecular gels with a mixture of an aqueous and an organic solvent, which

are known as ambidextrous gelators.4-5 Supramolecular gels are most commonly formed

with large amount of solvent (f.ex. H2O, MeOH, DMSO and etc.) immobilised in a

small amount of solid(s), which is the “gelator”. Heat and sonication is applied to

dissolve the gelator, sample is then left undisturbed to form a gel. In some cases gel

forms immediately and in other cases it could take up to a day or more. For the gel to

form the gelator molecules have to self-assemble to form 3D nanostructures to

immobilise the solvent molecules (Scheme 1.1).

Scheme 1.1: Description of how supramolecular gels are formed.

Supramolecular gels are responsive and customizable by mechanical, thermal and

chemical exterior stimuli, for instance acidity (pH), temperature, ultrasound and etc.

Another factor that could play a big role, is by increasing the viscosity that associates

with gel formation, which allows an alteration of thermal signal into a mechanical

response.

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1.1 Understanding metallogels architecture A gel can be identified by a simple inversion test. If the gravitational force doesn’t pull

the gel, then you have formed a legitimate gel. Another way to confirm it is with SEM

(scanning elelctron microscopy) imaging, which can get a clear image, as far down as at

the nanoscale, of its fibrous network.1-3 LMWGs are thermoreversible, which could be

confirmed by solvent to gel (sol-gel) transition. The sol-gel transition are analysed by

heating the compound in a particular solvent and cooling to room temperature. Once the

gel is formed, the process (heating and cooling cycle) is repeated to evaluate the

thermoreversibility. Generally, LMWGs gels are physical gels and are generally

thermoreversible. Chemical gels are formed via strong covalent interactions and are

generally not thermoreversible but have stronger networks, which can be modified more

easily. On the other hand, the strength of a metal-ligand coordination interaction lies

somewhere between being a strong covalent bond and that of being a non-covalent

interaction. Therefore, introducing metal coordination will result in coordination based

gels (metallogels), which will have the properties of either chemical or physical gels

depending on the circumstances.1

Recently, there has been an upsurge of interest in metal based supramolecular gels

(metallogels). These metal-containing LMWGs have strong coordination interactions

between the organic moiety and metal centre, which act as a key driving force in the

formation of the gel fibre network in combination with the various non-covalent

interactions. The gel fibres themselves can arise from the self-assembly of discrete

complexes, coordination polymers or cross-linked coordination polymers. Metallogels

can therefore be enhanced with other physicochemical properties of metals such as

color, magnetism, catalytic activity, emission and etc. Consequently, metallogels have

Figure 1.1: SEM images, which display fibrous network of Cu(OAc)2

. H2O gels of 4PNA in a) DMF/H2O and b) only in H2O.2

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Figure 1.2: Explains the structure of a) primary, b) secondary and c) tertiary structures of urea based supramolecular gel19

the tendency to function to a great deal of physical and chemical stimuli.1

It has been puzzling chemists in this field how the gel formation mechanism truly is.

But it’s possible to characterize the surface of these gels with various instruments such

as scanning-electron, transmission-electron and atomic force microscopy (SEM, TEM

and AFM). On Figure 1.1 there are 2 SEM images of copper acetate xerogels from Dr

Damodaran and co-workers work on metal gelation of N-(4-pyridyl)nicotinamide

(4PNA).2 The microscopic data from these instruments have revealed that there’s a

highly perplex 1D fibrous networks in dried gels (xerogels). These discoveries clearly

indicate that the gelator molecules accumulate into a 1D system that is held together

with various non-covalent interactions. These 1D fibers are twisted together and

connected to other fibers, which

reminiscences a net or a web resulting in a

3D network structure known as a self-

assembled fibrillar networks (SAFINs)

where all the solvent material are

immobilized, which results in a gel. It

should be mentioned that gel formation

could only take place when the

concentration of the gelator (minimum

gelator concentration (MGC)) is above a

critical threshold.5 Furthermore, the single

crystal structure of gelator can be

correlated to that of the gel state by comparing with the structures of xerogels (dried

gel).2 This falls under the field of crystal engineering, which is a very important factor

for designing LMWGs and the key structural features of gel-network formation in

LMWGs can be identified using supramolecular synthons such as amide and urea

moieties.15

a b c

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1.2 Amide based gelators and metallogels Amide groups play a big role in gel formation. The most important type of interactions

in biological systems are hydrogen bondings, they are non-covalent and are ideal to

construct supramolecular gels, which can be done via the strategy of self-assembly.

Each molecule contains an amide N−H donor and C=O acceptor (Figure 1.2). The main

building block of gel formation is the strong hydrogen bonding N−H···O=C, and self-

assemble, which can result in a polymeric fiber-like 3-D network.16 The amide groups

are also highly beneficial in immobilizing the solvent molecule, which is also a crucial

part in gel formation.14

Amide-functionalized components, which have a self-assembling system and gelators

such as pyridine are known to be responsive to external stimuli such as ultrasound,

acids and metal ions. When such an external stimuli takes place, a self-assembly can be

triggered by the introduction of f.ex. a solvent. For the purpose of interacting with metal

ions and acids to form gels, the pyridine is the preferred functional group of the

molecule. Despite the fact that there is a great variety of assemblies and gels which are

established on known pyridine-functionalized systems, the role of the pyridyl amide is

not fully understood when it comes down to the gelation and aggregation properties of

π-systems.17 But it is known that a metallogel can be formed when a pyridyl nitrogen

atom coordinates with a metal ion, as seen on Scheme 1.2.

It is also very important where the pyridyl nitrogen atoms are positioned in the aromatic

ring for gel formation. For example it has been reported that the ligand N-(4-

Scheme 1.2: Incorporation of a metal, which coordinates to the pyridyl nitrogen.18

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pyridyl)isonicotinamide form hydrogels, but if the isonicotinic group of N-(4-

pyridyl)isonicotinamide is replaced with a nicotinic group the ligand can form

metallogels.13, 21

Amides and urea moieties act in similar ways. Urea can hydrogen bond in a

monodentate and bidentate fashion to the oxygen of the neighboring urea, whereas the

amide can only hydrogen in a monodentate way (Figure 1.3; b). Similarly as for

pyridyl-amide based compounds, the pyridyl-urea based compounds can coordinate to a

metal through the pyridyl group, which will subdue the gel-hindering pyridyl-urea

hydrogen bonding interaction, which will allow the urea groups to form fibrils freely,

resulting in gel formation (Scheme 1.2; a and b).18

In this B.S project, amide motif have been chosen as supramolecular synthons and these

amide ligands will be coordinated to various metals to form 1-D chains, which will give

a fibre surface.15

Figure 1.3: a) Bidentate and monodentate hydrogen-bonding of urea. b) monodentate hydrogen-bonding of amide.

a b

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2 Aim and objective The aims of this BS project are:

1) Synthesis of functional ligands with amide motif

2) Synthesis of metallogelator and evaluate gelation properties

3) Structure property correlation

2.1 Strategy The initial objective of this project was to synthesize 4 different isomers of the organic

ligand (Scheme 2.1) and to observe if it is possible to form metallogels and/or metal

complexes (crystals) with various metal salts in solution.

Scheme 2.1: Reaction scheme of the synthesis of the organic ligands.

The procedure of how L1-L4 (names of the compounds can be found in the list of

abbreviations) were synthesized is described in the experimental section. It would be

ideal to incorporate a protecting group, an isopropyl ester, which would be a 3-step

synthesis for each individual isomer (see 3.2.1-3.2.4). Dr. Damodaran’s group has

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already found that pyridyl amide compounds are ideal to form metallogels.2 Therefore

making metallogels with ligands L1 through L4 will be the main goal of this project.

Furthermore, it is important to evaluate the strength of the supramolecular network of

these metallogels, which is done with a gelation test and Tgel experiments. A detailed

description of how these tests and experiments were conducted can be found in the

experimental section.

2.2 Importance of functional groups Ghosh and co-workers synthesized N-(4-pyridyl)nicotinamide (4PNA), which formed

gels and crystals with copper(II) salts.2 The functional groups of L1-L4 are different

from 4PNA, the nitrogen on the ring bound to the amine, is replaced with a carboxylate

group. It’s also crucial that the nitrogen atom of the pyridine ligand is at the right pH

level. Since addition of H+ will protonate the nitrogen atom and interrupt the metal-

ligand interactions, which are essential for the gel formation, and cause the gel to

transform into a solvent.3

Note to mention the properties of one of the other functional groups, the carboxylate,

which can also play a big role in formation of coordination polymers. Ligands

containing carboxylate are a certain type of a multifunctional unit. They can bind to

metal ions to form coordination polymers, but they can also behave as hydrogen bond

acceptors and/or donors. These hydrogen bonds can bridge the metal ions into

coordination polymeric structures and assemble them into higher dimension polymers,

from 1D to higher dimension networks.7

The importance of the amide is also very important. Its role was mentioned in details in

the introduction (1.2).

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3 Experimental

3.1 Material and methods All chemicals used as starting materials were purchased from commercial sources and

were used as supplied except solvents such as DCM, CHCl3 and THF, which were

freshly distilled. Each distillation took place over approximately 3 hour reflux. The

DCM was distilled with CaH2 to remove water from the solvent. The chloroform was

purified with distillation with P2O5 to remove water from the solvent. The THF was

distilled with pieces of pure sodium and benzophenone, which combined works as a

deoxygenation agent. When refluxed, the sodium and benzophenone makes the solution

turn purple which is an indication that there’s no trace of water in the THF. All water

used was deionised. 1H-NMR spectrums were recorded on a Bruker Advance 400

spectrometer. MS was also conducted on final products. The MS spectra are available in

the supplementary information section.

3.2 Synthesis of L1

We have tried various methods to synthesise L1. First method was to protect the

carboxylic acid group by converting it to isopropyl ester (Figure 3.1). The procedures

are given in details below.

Scheme 3.1: Step-by-step scheme of protecting and deprotecting of acid group.

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3.2.1 Synthesis of isopropyl 4-aminobenzoate and isopropyl 3-aminobenzoate

Thionyl chloride (e ml, 138 mmol) was added dropwise to a solution of ice-cooled

(0°C) 4-amino benzoic acid (5.07 g, 36.9 mmol) in iso-propanol (60 mL). This was

performed in anhydrous conditions and under N2 flow. After addition the temperature

was raised to 90 °C and allowed to reflux for 4 hours. In work up all the solvents were

evaporated and white solid, isopropyl 4-aminobenzoate, was collected.9 The same

procedure as above was conducted with 3-amino benzoic acid. The final product

isopropyl 3-aminobenzoate was obtained, which was a white solid as well.

3.2.2 Synthesis of nicotinoyl and isonicotinoyl chloride

Nicotinic or isonicotinic acid (2.1 g, 17.1 mmol) was added to a 100 mL 1-neck RB

flask, reaction was conducted under anhydrous conditions. Thionyl choride (10 mL,

137.5 mmol) was added and refluxed for 2 hours at 78°C. Excess thionyl chloride was

evaporated which left behind white acid chloride crystals.10

3.2.3 Synthesis of isopropyl 3- & 4-(nicotinamido)benzoate and isopropyl 3- & 4-(isonicotinamido)benzoate

To the acid chloride (1.0 eq.) 50 mL of distilled DCM was added, it did not completely

dissolve. The acid chloride from section 2.1.2 was dissolved in ~50 mL DCM and the

amine ester (0.9 eq.) from section 2.1.1 was dissolved in ~50 mL DCM as well, along

with triethyl amine (2.0 eq.). This solution was added dropwise to the ice-cooled (0 °C)

acid chloride. After addition of all the reactants the solution was allowed to stir

overnight which was then refluxed for 4 hours at 55°C. Work up: A solution of 5%

Na2(CO3)2 was added to dissolve the acid chloride and the triethyl amine salts to a pH

around 7. Finally it was centrifuged to obtain the final product, since filtration was

almost impossible due to the products viscosity.6

Only 2 of these 4 reactions were successful, isopropyl 4-(isonicotinamido)benzoate and

isopropyl 4(nicotinamido)benzoate. One was lost in an unfortunate accident and the

other simply didn’t form for unknown reasons.

10

Only 2 of these 4 reactions were successful, isopropyl 4-(isonicotinamido)benzoate and

isopropyl 4(nicotinamido)benzoate. One was lost in an unfortunate accident and the

other simply didn’t form for unknown reasons.

3.2.4 Synthesis of L1 and L4

This step involved a hydrolysis of the carboxylic isopropyl ester group and reclaiming

the initial –OH acid group. The product(s) (1 eq.) from section 2.1.3 was dissolved in

20mL THF, 5mL MeOH and a 1M NaOH (20eq.) solution. Stirred at RT overnight,

organic solvents evaporated, residue dissolved in H2O, washed with DCM and acidified

with 1M HCl to pH ≈ 6 in an ice bath, in an attempt to precipitate the product, which

was unsuccessful. Therefore the solution was evaporated via rotavapor. To get rid of the

NaCl that had formed, MeOH was added to the solid and filtered. Followed up with an

EtOAc/MeOH wash, the solid didn’t dissolve, therefor this partially dissolved solution

was filtered. The solid that was obtained from the solution and filtration were

characterized seperately.11

3.2.5 Different approach to synthesize L1

Same method was used, as in section 3.2.3, except chloroform (CHCl3) was used

instead of DCM (Scheme 3.2). The solid was washed with THF and DCM, and a light

yellow solid was collected. Characterization (1H-NMR and MS) of this first batch

(L1B1) confirmed that the ligand was formed and gelation studies showed promising

results. This was the 1st attempt with this method. In the following attempts, this was

observed.

Scheme 3.2: Reaction scheme, which shows the formation of L1.

11

In the 2nd attempt, there was always a small amount of SOCl2, which couldn’t be

distilled out. Therefore excess amount of triethylamine was used to neutralize the acid.

After adding the DCM to the acid chloride, along with triethylamine (3mL, 4 eq.), the

solution turned red. Next the 4-amino benzoic acid was added dropwise which resulted

in a gray-green solution along with white precipitate. After refluxing at 57 °C, the

solution turned to dark brown. Filtered and washed with THF and DCM. Dissolved

when washed with H2O due to its acidity. Therefore by adding the right amount of 5%

Na2CO3(aq) to bring the pH to around 7. A light brown solid was collected (L1B2).

Another successful batch (L1B3) was made with the same method as in the 2nd

attempt, which resulted in a brown solid as well. The 1H-NMR showed promising

results for this batch and the one before, but the gelation studies did not.

In the 4th attempt CHCl3 was used instead of DCM (just like in the 1st attempt).

Everything done the same here except the triethylamine (18mL, 24 eq.) diluted in

CHCl3 was added last. About 24 equivalents were added due to the pH level. It was

believed that the reaction couldn’t happen in highly acidic conditions. The solution

turned from white to yellow and finally black after this addition, which was a clear

indication of failure (as in 2nd and 3rd attempt). The product was therefore not

characterize, instead another final attempt to synthesize the ligand was conducted.

In the final successful attempt (L1B4) it was conducted just like in the previous attempt

(4th), except much less triethylamine (7mL) was added. It was diluted in CHCl3 and

added dropwise, until the solution turned slightly yellow. This was a crucial part for the

ligand to be able to form gels with certain metal salts. The final product was white and

its structure was confirmed by 1H-NMR and MS.

The focus was on L1 and L2, but mainly L1. The yield in percentages for the successful

reactions will be represented in Table 3.1.

12

Table 3.1: Yields from the successfully synthesized ligands (L1 and L2).

L1 L2

Batch Yield (%) Color Yield (%) Color

1 40 Yellow 70 Brown

2 80 Brown

3 92 Brown

4 15 White

C13O3N2H10 (L1): 1H-NMR (DMSO-d6, 400 MHz): δ 7.59 (dt, 1H), 7.91 (d, 2H), 7.97

(d, 2H), 8.31 (dt, 1H), 8.79 (d, 1H), 9.13 (s, 1H), 12.8 (s, 1H). 13C-NMR (DMSO-d6): δ

119.5, 123.6, 125.8, 130.2, 130.5, 142.9, 148.4, 151.9, 164.3, 166.84.

See chapter 6, Supplementary information, for NMR spectra.

3.3 Synthesis of L2

Multiple attempts were conducted to synthesize this isomer of the ligand; in total there

were 4 attempts. In the 1st attempt it was conducted almost the same as in section 3.2.5,

except only THF was used as a solvent and 10 equivalents of triethylamine was added.

After addition the solid did not completely dissolve. In the work-up the solid was

washed with THF and then H2O. 1H-NMR confirmed that the product was not formed.

In the 2nd attempt, in the work-up, it was washed and filtered with THF and DCM, the

white solid dissolved completely after washing it with H2O.

The same process took place in the 3rd attempt. The problem was with the pH, which

was too acidic.

In the 4th attempt (L2B1), by adding 5% Na2CO3 to neutralize the solution, the brown

product precipitated. Characterization (1H-NMR and MS) confirmed that the ligand was

formed.

The product triethylamine hydrochloric salt was visible on 1H-NMR. It’s highly soluble

in water, but a recrystallization was conducted on the solid in DMF/EtOH/H2O (1:2:2

v/v). The yield can be found in table 3.1.

13

C13O3N2H10 (L2): 1H-NMR (DMSO-d6, 400 MHz): δ 7.55 (t, 1H), 7.66 (dt, 1H), 7.76

(d, 1H), 8.10 (d, 1H), 8.40 (d, 1H), 8.47 (t, 1H), 8.84 (dd, 1H), 9.20 (s, 1H), 10.68 (s,

1H), 13.0 (s, 1H).

See chapter 6, Supplementary information, for NMR spectra.

3.4 Synthesis of metal complexes with L1

Since the ligand doesn’t dissolve in any solvent that are fairly volatile, such as

methanol, ethanol, water and etc. Only solvents such as DMSO or DMF were able to

dissolve the ligand. Water can’t be used to dissolve the metal salts, since addition of

water will most likely make the ligand precipitate immediately. Results are in Table 4.6.

14

4 Results and discussion

4.1 Synthesis As can be seen in the experimental section, the synthesis can be broken into two parts,

the protection & deprotection (3 step) method, and the direct synthesis (1 step) of the

ligand.

4.1.1 Synthesis of amino benzoic acid esters

The methods are carefully described in the experimental procedure section 3.2.1 - 3.2.4.

It was successful up until the deprotection step. The reaction is relatively simple and the

mechanism is shown in Scheme 4.1.

4.1.2 Synthesis of acid chloride

The reaction mechanism (Scheme 4.2) of the iso-/nicotinic acid chloride forms

hydrochloric acid salt with the iso-/nicotinic group and emits sulfur dioxide gas as a

side product.

Scheme 4.1: Mechanism of esterification of amino benzoic acid with thionyl chloride.

15

Scheme 4.2: Mechanism of the iso/nicotinic acid chloride.

4.1.3 Synthesis of L1-L4

The reaction mechanism (scheme 4.3) for the ligands formation is a Schotten Baumann

nucleophilic substitution.

Scheme 4.3: Mechanism of the formation of L1 to L4.

The amine reacts with the acid chloride to form a protonated intermediate. A base,

which in this case was triethylamine, was used as a catalyst to absorb the acidic proton

and which makes this whole reaction feasible. Once the base removes the proton, the

final product is made, along with a side product, which was a triethylamine

hydrochloric salt. After the ligand had been isolated from the synthesis it’s gelation

ability with various metal salts was tested. There are many variables that affect whether

a gel can be formed or not. Such as choice of solvent(s), solvent ratio (if the type of

solvents are more than 1), metal-ligand molar ratio, weight percentage (wt.%) of

gelators, temperature, pH (as mentioned before), sonication, mixing methods etc.

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4.4 Gelation studies of L1 with various metals The ligand from 3.2.5 (1st batch, L1B1) was screened for gel formation (table 4.1) with

various salts. All of the metal salts were soluble in H2O, but for the ligand it was

different. The ligand didn’t dissolve in water, methanol, ethanol, acetonitrile, DCM,

chloroform and etc. Only highly polar solvents such as DMSO and DMF dissolved the

ligand completely. Therefor the 1st gelation trial was conducted in 50% DMSO and 50%

H2O, where the ligand (1 eq.) is dissolved in DMSO and the metal salt (1 eq.) in H2O.

Table 4.1: Gelation studies of L1B1 with different metal salts in 1:1 DMSO/H2O (v/v) and 1:1 Metal:Ligand molar ratio.

Metal salts wt% Intial observation Final observation (24h) Cu(OAc)2·H2O 3.4 Blue-green S/PG Blue-green S/PG CuCl2 3.1 Blue-green G Blue-green G Cu(NO3)2·3H2O 3.9 Blue-green S Blue S Cu(ClO4)2·6H2Oa 2.7 Blue-green S Green S Cu(SO4)·5H2Ob 4.0 Blue-green S Green S Zn(NO3)2·6H2O 4.2 White P White P Zn(OAc)2·2H2O 3.6 White P White P Zn(Cl2) 3.0 White P White P Zn(SO4)·7H2O 4.2 White P White P Zn(BF4)·H2O 3.8 White P White P Cd(NO3)2·4H2O 4.4 White P White P Cd(OAc)2·2H2O 4.1 White P White P CdCl2 2.6 White G White G Cd(SO4)·

!! H2O 3.5 White P White P

FeSO4·7H2O 4.1 Yellow S Orange P FeCl2·4H2O 3.5 Yellow P Yellow P NiCl2·6H2O 3.8 Green S Green P Ni(NO3)2·6H2O 4.4 Green P Green P Co(OAc)·4H2O 3.9 Pink P Pink P CoCl2 3.8 Pink S Pink P Co(NO3)2·6H2O 4.3 Pink P Pink P MnCl2·4H2O 3.4 White P White P MnSO4·H2O 3.2 White P White P Mn(NO3)2·4H2O 3.9 White P White P Ni(OAc)2·4H2O 3.9 Blue P Green P S = solution, P = precipitate, PG = partial gel, G = gel. a Gelation experiments were performed in 9:1 DMSO/water (v/v). b Gelation experiments were performed in 8:2 DMSO/water (v/v).

From the results (Table 4.1) it’s clear that there are 3 metal salts that form gels or at

least partial gels with the ligand. Therefor the next step was to find the minimum weight

17

percentage (wt.%) where they form (see Table 4.2). There wasn’t enough of the ligand

(L1B1) gelator left to do further gelation tests for Cu(OAc)·H2O at higher

concentrations (wt%) and neither for CdCl2 nor ZnCl2.

Table 4.2: Gelation studies of L1B1 to find minimum wt% 1:1 DMSO/H2O (v/v) and 1:1 metal:ligand molar ratio

Metal salts wt% Initial observation Final observation (24h) Cu(OAc)2·H2O

4.0 Blue-green PG Blue-green PG 5.7 Blue-green PG Blue-green PG 7.6 Blue-green PG Blue-green G on bottom and

PG on top layer CuCl2

1.0 Green S Green S 1.9 Blue-green PG Blue-green PG 3.0 Blue-green G Blue-green G

S = solution, P = precipitate, PG = partial gel, G = gel

The gelation experiments with batches L1B2-B3 were not as successful as L1B1. It was

only possible to form gels with L1B2 if the aqueous solution of the metals was slightly

basic (pH = 7-8). It was slightly different for ligand L1B3, it did form gels with CuCl2,

but only within a couple of days after the ligand was synthesized. After a period of a

few days the ligand lost its ability to form (CuCl2) gels. The ligand to be washed again

in 5% NaHCO3 to reclaim their gelation ability with CuCl2 at 3 wt% (see results in sup.

inf. 6.6 and 6.7). Despite having tried recrystallizing the ligands in DMF:EtOH:H2O

(1:4:10 (v/v)) and different mixing methods of the ligand and metal salts, such as

dissolving the ligand and metal in the DMSO and then add the H2O, were unsuccessful.

The last batch, L1B4, was able to form stable gels with CuCl2 only, and since the yield

was low, there wasn’t much of the ligand left to conduct thorough gelation tests with

Cu(OAc)2·H2O since it only forms gels at higher weight percentages (+8wt%).

Although it was discovered that changing the metal-ligand ratio from 1:2 to 1:1 had a

great effect on the minimum wt% needed to form a gel. At least that was the case for the

CuCl2 gel. The minimum wt% for gel formation was 2.4 wt% in 1:1 ratio, but 3.0 wt%

in 1:2 ratio. For the CdCl2 it was previously discovered for L1B1 that it formed a gel at

2.6 wt% (Table 4.1). With L1B4 it did form immediately, but 24 hours later it wasn’t

gel anymore (Table 4.3).

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Table 4.3: Gelation studies of L1B4 with various metal salts

Metal salts wt% DMSO:H2O (v/v) M:L IO FO (24h) Cu(OAc)2·H2O 8.7 50:50 1:2 Blue PG White P CuCl2

2.4 70:30 1:1 Blue G Blue G 1.5 70:30 1:1 Blue S Blue S 2.4 80:20 1:1 Blue S Green S 2.4 50:50 1:1 Blue G Blue G 1.5 50:50 1:1 Blue S Blue P 3.0 50:50 1:2 Blue G Blue S/P 2.0 50:50 1:2 Blue S Blue P 2.5 50:50 1:2 Blue S Blue P

3.0 70:30 1:1 Blue S Blue S Cu(NO3)2·3H2O 4.8 80:20 1:1 Blue S Blue S 3.0 90:10 1:1 Blue S Blue S 2.8 70:30 1:1 White P White P 2.8 80:20 1:1 Clear S White P CdCl2 2.8 50:50 1:1 White PG White P 1.6 50:50 1:1 Clear S White P 2.1 50:50 1:1 Clear S White P Zn(OAc)2·2H2O 1.0 50:50 1:2 Clear S White P 3.0 50:50 1:2 Clear S White P S = solution, P = precipitate, PG = partial gel, G = gel, IO = Initial Observation, FO = Final Observation

The 3 gels that passed the inversion test can be seen on Figure 4.1.

Figure 4.1: Gels that passed the inversion test: a.) CuCl2, 1:1 M:L, 2.4 wt%, 50:50 DMSO:H2O. b.) CdCl2, 1:1 M:L, 2.6 wt%, 50:50 DMSO:H2O. c.) Cu(OAc)2·H2O, 1:1 M:L, 2.6 wt%, 50:50 DMSO:H2O.

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4.4 Tgel experiment on CuCl2 gel (L1B4) The main idea of Tgel experiments is to find the maximum temperature that the gel can

sustain. Once the maximum temperature is reached (Tmax), the gel structure collapses

and liquefies. The optimal CuCl2 metallogel to conduct this Tgel experiment on was the

2.4 wt% one, 1:1 metal:ligand ratio and 50:50 DMSO:H2O (v/v), from table 4.4. A

quantity of 3 identical gels were made in vials, a colored glass marble ball (~0.5 cm in

diameter) was placed carefully on top of the gel, and the vial was placed in an oil bath

which was then heated (Table 4.4).

Table 4.4: Tgel experiments with 2.4 wt% CuCl2 metallogels.

Entry Tmax (°C)

1 71

2 72

3 71

The average maximum temperature that the CuCl2 metallogel can sustain is

approximately 71°C. It did not form gel immediately after it was cooled, but after 24

hours it wasn’t a gel anymore.

4.5 Gelation studies of L2 The only batch (L2B1) that was successful for L2 had a brown distinctive color, which

from previous experience is an indication that there’s something wrong with the ligand.

Despite all of this, gelation test of L2B1 were performed with CuCl2. It was treated with

NaHCO3, just like for the other ligand, to make it slightly basic. But the gel didn’t form

with CuCl2, therefor it was assumed that it wasn’t able to form gels like batches 2 and 3

of L1.

4.6 Metal complexes with L1B1 There were several attempts to synthesize metal complexes (crystals) of various metal

salts with ligand L1B1. Dastidar and Paul reported that by converting the ligands to a

sodium salt would allow the ligand to be soluble in solvents such as ethanol and to

coordinate with the metal, which theoretically would form a single crystal.6

Synthesizing a sodium salt of the ligand was not successful. Therefore different

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approach was taken. DMF was used alone to dissolve the ligand and metal salt, and left

for 24 hours (table 4.5). The total volume of solvents was 1 mL. Metal:ligand ratio was

1:2, 0.025 mmol and 0.050 mmol.

Table 4.5: Synthesis of metal complexes (crystals) with L1B1

Entry Metal Salt Dissolved in IO FO (24h)

1 Cu(NO3)2·3H2O 100% DMF Green S Green S

2 Cu(NO3)2·3H2O 50:50 DMF:H2O Green P Green P 3 Cu(OAc)2·H2O 100% DMF Green S Green C

4 Zn(NO3)2·2H2O 100% DMF Clear S Clear S 5 Cd(OAc)2·2H2O 100% DMF Clear S Clear S

6 Cd(NO3)2·4H2O 100% DMF Clear S Clear S S = solution, P = precipitate, C = crystals IO = Initial Observation, FO = Final Observation

Entry 1 in Table 4.6 had crystals after about 24 hours. The crystals were observed under

a microscope and after careful examination it revealed that the crystals were too small

(micro-crystals). Therefor it was not possible to mount them and to analyse them via X-

rays to reveal its crystal structure.

4.7 SEM images of xerogels The gels that passed the inversion test were filtered and dried to obtain dry gels

(xerogels). To confirm that there is a fibrous network, which is characteristic for

metallogels, SEM imaging is a good method to clarify that. The equipment that was

used was JEOL JSM-6610LA. The fibrous network could not be seen, because there

seem to be an interference and blurriness when zoomed further in (Figure 4.2).

Figure 4.2: SEM images of M:L ratio 1:1 gels in DMSO/H2O a) CdCl2 b) CuCl2

c) Cu(OAc)2.H2O

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5 Conclusions The 26 chosen metal salts, which were tested for gelation with L1 revealed that there

were at least 3 metal salts that showed gelation abilities. The CuCl2 was the only gel

that was managed to recreate with more than just 1 batch. For CdCl2 it was only

successful to form a gel with the 1st batch (L1B1). At last for the Cu(OAc)2·H2O it

formed a partial gel after 24 hours and was completely a gel after 2 weeks, and that was

at about 8 wt%. It’s possible that it would form a gel after 24h if the wt% is increased

slightly above 8 wt%, but it’s very unpractical to form a gel at such a high wt% like this

compared to the other 2 gels that form at around 3 wt%. On the other hand, no structural

information was available since no single crystals were obtained. A lot of effort was put

into synthesising a ligand which was able to form metallogels, it was successful early

on, but didn’t succeed again until the very end. It was crucial that the catalyst base

(NEt3) was diluted and added last to the reaction. The low yield of L1B4 could be

explained by the fact that the thionyl chloride that was used had expired many years

ago, which could mean that an unknown amount of the thionyl chloride has tranformed

into HCl and SO2 gases. Also the SEM imaging of the xerogels did not give promising

results, the equipment simply could not get a clear picture of a fibril network.

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References 1. Jianyong Zhang, C.-Y. S., Metal-organic gels: From discrete metallogelators to

coordination polymers. Coordination Chemistry Reviews 2013, 257, 1373-1408. 2. Ghosh, D.; Lebedyte, I.; Yufit, D. S.; Damodaran, K. K.; Steed, J. W., Selective

gelation of N-(4-pyridyl)nicotinamide by copper(ii) salts. CrystEngComm 2015, 17 (42), 8130-8138.

3. Anthony Yiu-Yan Tam, V. W.-W. Y., Recent advances in metallogels. The Royal Society of Chemistry 2013, 42, 1540-1567.

4. Nandi S, A. H., Jakob B, Lange K, Ihizane R, Schneider MP., A Novel Class of Organo- (Hydro-) Gelators Based on Ascorbic Acid. Organic Letters 2011, 13, 1980-1983.

5. Tapas Kumar Adalder, U. K. D.; Joydeb Majumder, R. R., Parthasarathi Dastidar, Molecular and Crystal Engineering Approaches Towards the Design of Functional Supramolecular Gelators. Journal of the Indian Institute of Science 2014, 94 (1), 9-24.

6. Mithun Paul, P. D., Coordination polymers derived from pyridyl carboxylate ligands having an amide backbone: an attempt towards the selective separation of Cu(II) cation following in situ crystallization under competitive conditions. CrystEngComm 2013, 16, 7815-29.

7. Bao-Hui Ye, M.-L. T., Xiao-Ming Chen, Metal-organic molecular architectures with 2,2′-bipyridyl-like and carboxylate ligands. Coordination Chemistry Reviews 2005, 249, 545-565.

8. L. Z. Rogovina, V. G. V. e., E. E. Braudo, Definition of the Concept of Polymer Gel. Polymer Science 2008, 50 (1), 85-92.

9. Ravi Naik, C. J., Hyeyoung Min, Hyun Kyung Choi, Kyung Hoon Min, Kyeong Lee, Synthesis and bioactivity of novel adamantyl derivatives as potent MDR reversal agents. Korean Chemical Society 2011, 32 (12), 4444-4446.

10. Zhonglei Wang, L. Y., Shuai Cui, Yingxi Liang and Xiaohua Zhang, Synthesis and Anti-hypertensive Effects of the Twin Drug of Nicotinic Acid and Quercetin Tetramethyl Ether. Molecules 2014, 19 (4), 4791-4801.

11. Edwards, M. P. K., Robert Arnold, Preparation of aryl and heteroaryl fused lactams as antitumor agents. PCT Int. Appl 2014, 259. CODEN:PIXXD2.

12. Kartha, K. K.; Praveen, V. K.; Babu, S. S.; Cherumukkil, S.; Ajayaghosh, A., Pyridyl-Amides as a Multimode Self-Assembly Driver for the Design of a Stimuli-Responsive pi-Gelator. Chemistry, an Asian journal 2015, 10 (10), 2250-6.

13. Kumar, D. K.; Jose, D. A.; Dastidar, P.; Das, A., Nonpolymeric Hydrogelator Derived from N-(4-Pyridyl)isonicotinamide. Langmuir 2004, 20 (24), 10413-10418.

14. Sengupta, S.; Mondal, R., A novel low molecular weight supergelator showing an excellent gas adsorption, dye adsorption, self-sustaining and chemosensing properties in the gel state. RSC Advances 2016, 6 (17), 14009-14015.

15. Li, A.-F.; Wang, J.-H.; Wang, F.; Jiang, Y.-B., Anion complexation and sensing using modified urea and thiourea-based receptors. Chemical Society Reviews 2010, 39 (10), 3729-3745.

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16. Rao, M. R.; Sun, S.-S., Supramolecular Assemblies of Amide-Derived Organogels Featuring Rigid π-Conjugated Phenylethynyl Frameworks. Langmuir 2013, 29 (49), 15146-15158.

17. Kartha, K. K.; Praveen, V. K.; Babu, S. S.; Cherumukkil, S.; Ajayaghosh, A., Pyridyl-Amides as a Multimode Self-Assembly Driver for the Design of a Stimuli-Responsive π-Gelator. Chemistry – An Asian Journal 2015, 10 (10), 2250-2256.

18. Meazza, L.; Foster, J. A.; Fucke, K.; Metrangolo, P.; Resnati, G.; Steed, J. W., Halogen-bonding-triggered supramolecular gel formation. Nature Chemistry 2013, 5 (1), 42-47.

19. L.A. Estroff and A.D. Hamilton, Chemical Reviews, 2004, 104, 1201-1

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6 Supplementary information

6.1 1H-NMR of compounds in experimental section 3.1.1 – 3.1.4

Figure 6.1: 1H-NMR of isopropyl 4-aminobenzoate in CDCl3

25

Figure 6.2: 1H-NMR of isopropyl 3-aminobenzoate in CDCl3

26

Figure 6.3: 1H-NMR of isopropyl 4-(nicotinamido)benzoate in CDCl3

27

Figure 6.4: 1H-NMR of isopropyl 4-(isonicotinamido)benzoate in CDCl3

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6.2 1H-NMR of compounds in experimental section 3.2

Figure 6.5: 1H-NMR of 4-(nicotinamido)benzoic acid (L1B1) in DMSO-d6

29


30


31


32

6.3 1H-NMR of L2B1 in experimental section 3.3


33

6.4 13C-NMR of L1B4

Figure 6.10: 13C-NMR of 4-(nicotinamido)benzoic acid (L1B4) in DMSO-d6

34

6.5 Mass spectroscopy

Figure 6.11: MS of 4-(nicotinamido)benzoic acid (L1B1) in methanol

35


36


37


38


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6.6 Gelation studies with 4-(nicotinamido)benzoic acid (L1B2)

Table 6.1: Gelation studies of L1B2, 1:1 DMSO/H2O (v/v) and 1:2 metal:ligand molar ratio

Metal salts wt% IO FO (24h) 1 drop addition of 5% Na2CO3(aq)

Cu(NO3)2·3H2O

5.2 Brown P Brown P Brown P 6.2 Brown P Brown P Brown PG

Cu(ClO4)·6H2Oa

4.1 Brown P Brown P Brown P 5.7 Brown P Brown P Brown P 7.0 Brown P Brown P Brown G

5.2 Brown P Brown P Brown P Zn(NO3)2·3H2O 6.8 Brown P Brown P Brown P 8.2 Brown P Brown P Brown G 5.1 Brown P Brown P Brown P Zn(OAc)2·2H2O 6.7 Brown P Brown P Brown P 8.3 Brown P Brown P Brown P 5.2 Brown P Brown P Brown G ZnCl2 6.5 Brown P Brown P Brown G 7.8 Brown P Brown P Brown G S = solution, P = precipitate, PG = partial gel, G = gel, IO = Initial Observation, FO = Final Observation, a = 9:1 DMSO:H2O

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6.7 Gelation studies with 4-(nicotinamido)benzoic acid (L1B3) Table 6.2: Gelation studies of L1B3, 1:1 DMSO/H2O (v/v) and 1:2 metal:ligand molar ratio

Metal salts wt% IO FO (24h) Cu(NO3)2·3H2O 5.7 Green S Blue P Cu(NO3)2·3H2O 8.6 Green S Blue P Cu(NO3)2·3H2Oa 5.7 Green S Blue P Cu(ClO4)·6H2O 7.0 Brown P Brown P Zn(NO3)2·3H2O 4.6 Brown P Brown P CdCl2 2.9 Brown P Brown P CdCl2

b 3.9 Brown PG Brown PG CdCl2

a 3.0 Brown S Brown P CdCl2

a & b 3.0 Brown S Brown P CdCl2

a 4.2 Brown S Brown PG CdCl2

c 3.9 Brown S Brown P Zn(OAc)2·2H2Ob 7.6 Brown P Brown P S = solution, P = precipitate, PG = partial gel, G = gel, IO = Initial Observation, FO = Final Observation, a = L1B1, b = 0.100mL Na2CO3 (aq) in 20 mL H2O, c = 8:2 DMSO:H2O

Table 6.3: Gelation studies of L1B3, 1:1 DMSO/H2O (v/v) and 1:1 metal:ligand molar ratio

Metal salts wt% IO FO (24h) CuCl2

a

CuCl2 2.9 Brown S/PG Brown PG 2.4 Brown G Brown G

CdCl2 2.4 Brown S Brown PG CdCl2 3.4 Brown PG Brown PG CdCl2

b 3.9 Brown S Brown P Cu(OAc)2·H2Ob 7.8 Brown P Green-blue P Cu(ClO4)2·6H2O 7.6 Brown P Brown P Zn(OAc)2·2H2Ob 6.5 Brown P Brown P Cd(OAc)2·2H2Ob 6.1 Brown P Brown P S = solution, P = precipitate, PG = partial gel, G = gel, IO = Initial Observation, FO = Final Observation, a = L1B2, b = 2/3 DMSO:1/3 H2O, c = 8:2 DMSO:H2O

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Synthesis, Characterization and Structural Analysis of ... thesis_FINAL.pdf · Figure 6.6 1H-NMR 4-(nicotinamido)benzoic acid (L1B2) in DMSO-d6 29 Figure 6.7 1H-NMR 4-(nicotinamido)