Properties of Coordination Compounds

Part 1 (1/3)

Applications of Crystal Field Theory

Dr. Christoph Sontag University of Phayao 2017

1

2

Coordination Compounds

3

Factors determining the type of bonds

(1) Oxidation number of the metal ox.no. 0 indicates a covalent M-L bond

(2) Coordination number -> Coordination compounds show the appropriate number of ligands, in contrast to ionic compounds Cu(SO4) as salt and as coordination compound:

4

Common Coordination numbers

early middle Co-Ni late

4 6 4 2 5

Which category of compound ?

Fe(CO)5 ox.no. cat:

FeCl3 ox.no. cat: (in water: pH 3)

K3Fe(CN)6 ox.no. cat:

CuSO4 ox.no. cat:

Cu(CN) 4 (2-) ox.no. cat: Cu(OAc)2

(2-) ox.no. cat:

6

Example

A) [Cr(NH3)3Cl3] B) [Cr(NH3)6]Cl3 C) Na3[Cr(CN)6] D) Na3[CrCl6]

Which of these compounds will form a precipitation with AgNO3 ?

(A precipitation with Ag+ + Cl- AgCl occurs only when free Cl- ions are present)

7

Review: CFT

Applications of Crystal Field Theory

8

Crystal Field Theory Review

http://wwwchem.uwimona.edu.jm/courses/CFT.html 9

Examples of 0 values

10 Shriver/Atkins Chap.20

(1) Compare CuSO4 and CuSO4*5H2O: Why is one white, the other blue ?

(2) Compare FeCl3*6H2O with Fe(CO)5: One is a solid, water soluble and has a green color, the other is a colorless liquid, immiscible with water. How about the nature of the bonds ?

(3) CFT: why is K4Fe(CN)6 yellow and K3Fe(CN)6 red ? Hint: which color/energy is absorbed – how can we explain the energy absorbed ?

(4) The ionic radius of M(2+) ions should decrease linear, but instead some elements have a smaller radius – means that the distance M(2+) – Cl(-) is smaller than expected. 11

http://www.youtube.com/watch?v=LydEaN8-WJ8 12

Spectrochemical series

13

Conclusions from CFT

14

Extension: LFT

15

pi-donor ligands => low splitting

16

pi-acceptor ligands => high splitting

17

Symmetry Symbols

http://www.webqc.org/symmetrypointgroup-td.html 18

Which symmetry do the 5 d-orbitals in a tetrahedron have ?

19

Conclusions from LFT

20

(1) Find the configuration (as tx2ge

yg / ext2

y), the number of unpaired electrons and the LFSE (in terms of ∆o / ∆t and P)

(2) Which of the following complexes has higher LFSE:

(h) [MnF6]3- i) [NiBr4]

2- j) [Fe(CN)6]4-

21

Applications of CFT

(1) Electronic spectra (2) Hydration energies (3) Lattice energies (4) Ionic radii (5) Spinel types

22

(1) Electronic Spectra (example)

Each peak in the spectrum (λ <-> ν ) corresponds to a change in the electronic state (Shriver/Atkins p.576) 23

Find ∆o from Tanabe-Sugano diagrams

∆/B

E/B V(H2O)6

2+ shows 2 peaks at 17200 and 25600 cm-1

(1) Get E-ratio: E2/E1 = 1.49 (2) Find by trial and error this ratio in the diagram => ∆/B we find here a value of 40/27 = 29 (3) From this we find B: E2 = 25600 = 40 *B E1 = 17200 = 27 *B => B = 640 cm-1 (4) When B is know, then ∆o = 29 * 640 cm-1 = 18600 cm-1 24

http://www.chem.uky.edu/courses/che610/JPS_Spring_2007/PS2_2007key.pdf

Self-study:

25

Energy ratios: E2/E1 = 1.8 E3/E1 = 3.05 E3/E1 = 1.68 Now we move on the x-axis until we find this ratio in the y values again (approximately !) => ∆/B = 10 from that we get B: E3/B = 29 (graph) => B = 896 cm-1 => ∆o = 10 * 896 cm-1 = 8960 cm-1

(more exact: take the average for all 3 found B values) 26

-> B= 25700 / 41 = 628 cm-1 -> v3 = 59 * B = 37000 cm-1 27

(2) Hydration energies

28

Example

Find the solution enthalpy for CaCl2: -> we can look up the HYDRATION energies for both ions:

-> the LATTICE energy for CaCl2 is +2258 kJ mol-1

http://www.chemguide.co.uk/physical/energetics/solution.html 29

Lattice Energy

Hydration Energy

30

http://www.youtube.com/watch?v=awD1qa7TF4A 31

Example: Ti(H2O)6 2+

What is the additional hydration energy for 1 mol due to the 2 d electrons? (Δo = 8000 cm-1) (1 cm-1 = 0.012 kJ/mol)

32

(3) Lattice energies Lattice Energy is used to explain the stability of ionic solids = the energy required to break apart an ionic solid and convert its component atoms into gaseous ions -> cannot be measured directly

Born-Haber cycle

33

Experimental data vs. calculated for MCl2 high-spin compounds according to the Born-Haber Cycle

34

Example

What is the additional Lattice Energy for VCl2 due to the d electrons in Vanadium ion ? (Δo = 5500 cm-1) (1 cm-1 = 0.012 kJ/mol)

35

(4) Ionic Radii M(2+) --- O

36

Ionic radii MCl2

37

Many ionic radii are smaller than expected – if the ion gets additional stabilization energy from CFSE

M2+ ions in water are in a weak field => they are all high-spin Then we get 2 minima in the radii at V2+ with 3 electrons in the t2g levels and Ni2+ with 6 electrons in t2g For low-spin there is only one minima at Fe2+ with 6 electrons in t2g

38

Example

Estimate which M-O distance is the shortest: a) Fe2O3 (low spin)

b) FeO (low spin)

c) Fe(H2O)6 3+ (high spin)

39

(5) Spinels (gemstones)

Spinels = crystals formed by mixed oxides, originally used for MgAl2O4

In a closed packed solid, there are tetrahedral and octahedral “holes” filled with a metal ion.

“ cubic closed packing”

(https://www.youtube.com/watch?v=U_n7DyCqv6U)

40

Example

What is the oxidation number of Fe in Fe3O4 ?

41

“normal”: A in Td , B in Oh holes

Fe3O4 is a spinel type : Fe2+ (Fe3+ )2 O4

“inverse”: A in Oh, 1/2B in Td and 1/2B in Oh

(neg

lect

pa

irin

g e

ner

gy

P)

http

://ww

w.everyscien

ce.com

/Ch

em

istry/Ino

rganic/

Crystal_an

d_Ligan

d_Fie

ld_

Theo

ries/e.1

01

6.p

hp

“Magnetite”

42

If M3+ has a higher CFSE than M2+ in an octahedral field, these ions will prefer octahedral holes and forms a “normal” spinel.

Predict the structure for Mn3O4

43

Applications for Spinels

Spinel Ferrites M2+ Fe3+2 O4

Fe-O framework

Spinel Aluminates M2+ Al3+2 O4

Al-O framework

44

https://www.youtube.com/watch?v=U_n7DyCqv6U 45

46

47

Visualization of molecules and orbitals www.chemtube3d.com

48

3D structures of crystals

Fe(2+) Fe(3+)

49

50