1. Transition Metals, Compounds and Complexes or
Electronic Spectroscopy of Transition Metal Complexes
Dr. E.R. Schofield
Lecture 6: Tanabe-Sugano diagrams and Charge Transfer Transitions
Tanabe-Sugano diagrams
Calculating D, E and B
d0 and d10 ions
Charge Transfer transitions

2. Tanabe-Sugano diagram for d3 ions
n1 = cm-1 visible
n2 = cm-1 visible
n3 = obscured by CT transition
[Cr(H2O)6]3+: Three spin allowed transitions
E/B
= 1.41
17 400
= 24
D/B = 24
n3 = 2.1n1 = 2.1 x
 n3 = cm-1
D/B

3. Calculating n3
n1 = cm-1
n2 = cm-1
E/B
When n1 = E = cm-1
E/B = 24
so B = 725 cm-1
When n2 = E = cm-1
E/B = 34
so B = 725 cm-1
E/B = 34 cm-1
E/B = 24 cm-1
If D/B = 24
D = 24 x 725 = cm-1
D/B
= 24

4. n1 = cm-1 visible
n2 = cm-1 visible
n3 = obscured by CT transition
Energy diagram for octahedral d3 complex
4T1g
10 Dq
2 Dq
6 Dq x
15 B'
For Oh d3, Do = n1 = cm-1
Do / B = 24
B = 725 cm-1
4T1g
4T2g
4A2g

5. Charge Transfer Transitions
d0 and d10 ions
d0 and d10 ion have no d-d transitions
Zn2+ d10 ion
white
TiF4 d0 ion
TiCl4 d0 ion
TiBr4 d0 ion
TiI4 d0 ion
white
white
orange
dark brown
[MnO4]- Mn(VII) d0 ion
[Cr2O7]- Cr(VI) d0 ion
extremely purple
bright orange
[Cu(MeCN)4]+ Cu(I) d10 ion
[Cu(phen)2]+ Cu(I) d10 ion
colourless
dark orange
Charge Transfer Transitions

6. Metal-to-ligand charge transfer MLCT transitions
Ligand-to-metal charge transfer
LMCT transitions
Charge Transfer Transitions
d-d transitions
Lp*
eg*
t2g* Md Lp Ls

7. Selection rules
CT transitions are spin allowed and Laporte allowed
Transitions occur between metal based orbitals with d-character and ligand based orbitals with p-character
Dl = ± 1
Transitions occur from a singlet GS to a singlet ES
DS = 0
CT transitions are therefore much more intense than d-d transitions

8. LMCT Transitions
spin-allowed; Laporte allowed
[MnO4]-, dark purple
LMCT = ligand to metal charge transfer
e- rich ligand
O2-, Cl-, Br-, I-
e- poor metal (electropositive), high charge
Cr(III), d3 ion, Mn(VII), d0 ion

9. MO diagram of MnO4- L(t1)  M(e) 17 700 cm-1
L(t1)  M(t2*) cm-1
L(t2)  M(e) cm-1
L(t2)  M(t2*) cm-1 M
ML4 4L a1 t2 t1 e
t2*
a1* t* t2
(n+1)p a1
(n+1)s Dt
e, t2 nd
t1 ,t2 p
a1 ,t2 s

10. spin-allowed; Laporte allowed LMCT Transitions
[CrCl(NH3)5]2+, Cr(III), d3
LMCT 4 3
log(e/L mol-1 cm-1) 2
d-d
d-d 1
200
( cm-1)
400
( cm-1)
600
( cm-1)
l / nm
Identifying charge transfer transitions
Intensity
Solvatochromism - variation in absorption wavelength with solvent

11. e Charge-Transfer Transitions: MLCT spin-allowed; Laporte allowed
l / nm
400
500
600
300
100
200
lmax = 458 nm
[Cu(phen)2]+, dark orange
MLCT = metal to ligand charge transfer
e- rich metal, low charge, lower OS
Cu(I), d10 ion
p-acceptor ligand with low-lying p* orbitals
1,10-phenanthroline

12. e Charge-Transfer Transitions: MLCT spin-allowed; Laporte allowed
p-p*
lmax = 452 nm
MLCT
[Ru(bpy)3]2+, bright orange
200
300
400
500
l / nm
MLCT = metal to ligand charge transfer
e- rich metal, low charge, lower OS
Ru(II), d6 ion, low spin
p-acceptor ligand with low-lying p* orbitals
2,2'-bipyridine

13. Interelectron repulsion Limits of LFT – existence of electronic states
Russel-Saunders coupling Collecting microstates into terms
Using Hund's rules  GS and ES with same multiplicity
Effect of LF on free ion terms Orgel diagram for d1, d4, d6, d9 ions [Ti(OH2)6]3+
Orgel diagram for d2, d3, d7, d8 ions [Ni(OH2)6]2+
Calculating D, x and B' [Co(OH2)6]2+, [CoCl4]2-
Racah parameters in free ions and complexes
The Nephelauxetic effect
Orgel diagram for d5 ions [Mn(OH2)6]2+
Spin and Laporte Selection Rules Selection rules for Oh and Td complexes
Lifting selection rules
Origin of band broadening [Ni(OH2)6]2+, [Mn(OH2)6]2+, [Ti(OH2)6]3+
Tanabe-Sugano diagrams Low spin complexes [Mn(CN)6]4-
Calculating E, B' and D [Cr(OH2)6]3+, [V(OH2)6]3+
CT transitions MLCT, LMCT [Cu(phen)2]+, [Ru(bpy)3]2+, [MnO4]-