2. A/Prof Adam Bridgeman CHEM2402/2912/2916 [Part 2]
Ligand-Field Theory and Reaction Kinetics
A/Prof Adam Bridgeman
Room: 222
Office Hours: Monday 2-4pm, Wednesday 2-4pm
Other times by appointment or by chance

3. Where Are We Going…?
Shriver & Atkins, ‘Inorganic Chemistry’, OUP, 4th Edition, 2006
Week 4: Electronic Spectroscopy
Jahn-Teller effect
Electronic spectra of multi-electron atoms
Nephelauxetic effect and the spectrochemical series
Selection rules
Charge transfer transitions
Week 5: Bonding in Complexes, Metalloproteins and Materials
π-Donor and π-Acceptor Ligands
Metal-metal bonding in clusters and solids
Role of ligand-field effects in electrochemistry
Week 6: Kinetics and Ligand-Field Effects
Differential rate laws
Ligand substiution reactions

4. By the end of week 4… Ligand-field (‘d-d’) spectroscopy
be able to predict/explain number of bands for d1-d9 (high-spin)
be able to calculate Doct for d1, d3, d4, d6, d7, d8 and d9
be able to explain differences in band intensity (spin forbidden, orbitally forbidden, Laporte forbidden)
be able to explain the appearance of charge transfer transitions
be able to explain and predict the occurance of the Jahn-Teller effect and its consequences (structural, spectroscopic, reaction rates)
Resources
Slides for lectures 1-3
Shriver and Atkins “Inorganic Chemistry” Chapter 19 (4th Edition)

5. Schedule
Lecture 1: Electronic absorption spectroscopy Jahn-Teller effect and the spectra of d1, d4, d6 and d9 ions
Lecture 2: Interpreting electronic spectra Interelectron repulsion and the nephelauxetic effect
Lecture 3: Interpreting electronic spectra Selection rules and charge transfer transitions
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.

6. Revision – Ligand-Field Splitting
In the absence of any ligands, the five d-orbitals of a Mn+ transition metal ion are degenerate
Repulsion between the d-electrons and ligand lone pairs raises the energy of each d-orbital
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
JKB – Lecture 3, S & A 19.1

7. Revision – Ligand-Field Splitting
Two of the d-orbitals point along x, y and z and are more affected than the average
Three of the d-orbitals point between x, y and z and are affected less than the average
The ligand-field splitting
(eg)
(t2g)
(Doct) eg
Doct
t2g
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
JKB – Lecture 3, S & A 19.1

8. Electronic Spectra of d1 Ions
A d1 octahedral complex can undergo 1 electronic transition
The ground state (t2g)1 comprises three degenerate arrangements
The excited state (eg)1 comprises two degenerate arrangements
The electronic transition occurs at Doct eg eg
Ti3+(aq)
Doct
t2g
t2g
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
ground state
excited state
JKB – Lecture 3, S & A 19.3

9. Electronic Spectra of High Spin d4 Ions
A high spin d4 octahedral complex can also undergo just 1 transition
The ground state (t2g)2(eg)1 comprises two degenerate arrangements
The excited state (t2g)2(eg)2 comprises three degenerate arrangements
The electronic transition occurs at Doct
No other transitions are possible without changing the spin eg eg
Cr2+(aq)
Doct
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
t2g
t2g
ground state
excited state
JKB – Lecture 3, S & A 19.3

10. Electronic Spectra of High Spin d6 and d9 Ions
High spin d6 and d9 octahedral complexes can also undergo just 1 transition
The electronic transition occurs at Doct
No other transitions are possible changing the spin d6 d9
ground state
excited state
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
ground state
excited state
Cu2+(aq)
Fe2+(aq)

11. Effect of Distortion on the d-Orbitals tetragonal elongation
Pulling the ligands away along z splits eg and lowers the energy of dz2
It also produces a much smaller splitting of t2g by lowering the energy of dxz and dyz
Doct >>> d1 >> d2 eg d1
Doct
t2g d2
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
tetragonal elongation
JKB – Lecture 6, S & A p467

12. Which Complexes Will Distort?
Relative to average: t2g go down by 0.4Doct in octahedral complex
Relative to average: eg go up by 0.6Doct in octahedral complex
Relative to average dz2 is stablilized by ½d1 and dx2-y2 is destablilized by ½d1
Relative to average dxz and dyz are stablilized by ⅔d2 and dxy is destablilized by ⅓d2
+½d1 eg
+0.6 Doct d1
-½d1
Doct
+⅔d2
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter. d2
t2g
-0.4 Doct
-⅓d2
octahedron
distorted octahedron

13. Which Complexes Will Distort? Doct >>> d1 >> d2dn
configuration
degeneracy
LFSE
stabilized?
distortion
t2g eg 1 1 3
-0.4Doct d2
yes
small
+½d1 eg
+0.6 Doct
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
-½d1
+⅔d2
t2g
-0.4 Doct
-⅓d2

14. Which Complexes Will Distort? Doct >>> d1 >> d2dn
configuration
degeneracy
LFSE
stabilized?
distortion
t2g eg 1 2 3 4 5 1 3
-0.4Doct d2
yes
small 2 3
-0.8Doct d2
yes
small 3 1
-1.2Doct no no 3 1 2
-0.6Doct - 0.5d1
yes
large 3 2 1 no
none
+½d1 eg
+0.6 Doct
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
-½d1
+⅔d2
t2g
-0.4 Doct
-⅓d2

15. Which Complexes Will Distort? Doct >>> d1 >> d2dn
configuration
degeneracy
LFSE
stabilized?
distortion
t2g eg 1 2 3 4 5 6 7 8 9 1 3
-0.4Doct d2
yes
small 2 3
-0.8Doct d2
yes
small 3 1
-1.2Doct no no 3 1 2
-0.6Doct - 0.5d1
yes
large 3 2 1 no
none 4 2 3
-0.4Doct d2
yes
small 5
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter. 2 3
-0.8Doct d2
yes
small 6 2 1
-1.2Doct no no 6 3 2
-0.6Doct - 0.5d1
yes
large

16. Which Complexes Will Distort? Doct >>> d1 >> d2
Low spin: dn
configuration
degeneracy
LFSE
stabilized?
distortion
t2g eg 4 5 6 7 1
+½d1 eg
+0.6 Doct
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
-½d1
+⅔d2
t2g
-0.4 Doct
-⅓d2

17. Which Complexes Will Distort?
Large distortions (always seen crystallographically) :
high spin d4
low spin d7 d9
Cr2+
Co2+
Cu2+
Small distortions (often not seen crystallographically): d1 d2
low spin d4
low spin d5
high spin d6
high spin d7
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.

18. Any molecule with a degenerate ground state will distort
Jahn-Teller Theorem
This is a general result known as the Jahn-Teller theorem:
Any molecule with a degenerate ground state will distort
antibonding
bonding
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter. +

19. Effect on Spectroscopy
From Slide 6, there is one d-d transition for an octahedral d1 ion
From Slide 15, a d1 complex will distort and will not be octahedral
There are now 3 possible transitions
(A) is in infrared region and is usually hidden under vibrations
(B) and (C) are not usually resolved but act to broaden the band eg
Ti3+(aq)
(B)
(C)
Demos: charles law (2.3), CO2 density (2.1), star wars (4.3)
Brief mention of 3 states of matter.
t2g
(A)
(B)
(C)

20. Summary By now you should be able to....
Show why there is a single band in the visible spectrum for d1, high spin d4, high spin d6 and d9 octahedral complexes
Obtain the value of Doct from the spectrum of these ions
Show the electronic origin of the (Jahn-Teller) distortion for high spin d4, low spin d7 and d9 octahedral complexes
Predict whether any molecule will be susceptible to a Jahn-Teller distortion
Explain how the Jahn-Teller effect leads to broadening of bands in the UV/Visible spectrum
Next lecture
Effects of interelectron repulsion
Very important equation - one that you need to remember
surely this should depend on the gas ? … No, as we’ll see soon

21. Practice Very important equation - one that you need to remember
surely this should depend on the gas ? … No, as we’ll see soon

22. Practice Very important equation - one that you need to remember
surely this should depend on the gas ? … No, as we’ll see soon