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Coordination Chemistry
Electronic Spectra of Metal Complexes

Electronic spectra (UV-vis spectroscopy)

1

Electronic spectra (UV-vis spectroscopy)

hν

ΔE

The colors of metal complexes

2

Electronic configurations of multi-electron atoms
What is a 2p2 configuration?
n = 2; l = 1; ml = -1, 0, +1; ms = ± 1/2

Many configurations fit that description

These configurations are called microstates
and they have different energies
because of inter-electronic repulsions

3

Electronic configurations of multi-electron atoms
Russell-Saunders (or LS) coupling

For each 2p electron
n = 1; l = 1
ml = -1, 0, +1
ms = ± 1/2

For the multi-electron atom
L = total orbital angular momentum quantum number
S = total spin angular momentum quantum number
Spin multiplicity = 2S+1
ML = ∑ml (-L,…0,…+L)
MS = ∑ms (S, S-1, …,0,…-S)

ML/MS define microstates and L/S
define states (collections of microstates)
Groups of microstates with the same
energy are called terms

Determining the microstates for p2

4

Spin multiplicity 2S + 1

Determining the values of L, ML, S, Ms for different terms

1S

2P

5

Classifying the microstates for p2

Largest ML is +2,
so L = 2 (a D term)
and MS = 0 for ML = +2,
2S +1 = 1 (S = 0)
1D
Next largest ML is +1,
so L = 1 (a P term)
and MS = 0, ±1/2 for ML = +1,
2S +1 = 3
3P

Spin multiplicity = # columns of microstates

Largest ML is +2,
so L = 2 (a D term)
and MS = 0 for ML = +2,
2S +1 = 1 (S = 0)
1D

One remaining microstate
ML is 0, L = 0 (an S term)
and MS = 0 for ML = 0,
2S +1 = 1
1S

Next largest ML is +1,
so L = 1 (a P term)
and MS = 0, ±1/2 for ML = +1,
2S +1 = 3
3P
ML is 0, L = 0
2S +1 = 1
1S

6

Energy of terms (Hund’s rules)

Lowest energy (ground term)
Highest spin multiplicity
3P term for p2 case
3P

has S = 1, L = 1

If two states have
the same maximum spin multiplicity
Ground term is that of highest L

Determining the microstates for s1p1

7

Determining the terms for s1p1

Ground-state term

Coordination Chemistry
Electronic Spectra of Metal Complexes
cont
...
complex

Tet complex

1S

t2g0eg0

e0t20

d1

2D

t2g1eg0

e1t20

d2

3F

t2g2eg0

e2t20

d3

4F

t2g3eg0

e2t21

d4

5D

t2g3eg1

e2t22

d5

6S

t2g3eg2

e2t23

d6

5D

t2g4eg2

e3t23

d7

4F

t2g5eg2

e4t23

d8

3F

t2g6eg2

e4t24

d9

2D

t2g6eg3

e4t25

d10

Holes in d5
and d10,
reversing
energies
relative to
d1

Free ion GS

d0

1S

t2g6eg4

e4t26

Holes: dn = d10-n and neglecting spin dn = d5+n; same
splitting but reversed energies because positive
...


d4 ≡ d9

Orgel diagram for d1, d4, d6, d9
Eg! or E!
T2g or T2!
!
Energy

D!

T2g! or T2!
Eg or E!
!
Δ

d1, d6 tetrahedral
d4, d9 octahedral

0!

d1, d6 octahedral
d4, d9 tetrahedral

Δ

ligand field strength

12

Orgel diagram for d2, d3, d7, d8 ions
Energy

A2 or A2g
T1 or T1g

T1 or T1g

P
T1 or T1g

T2 or T2g

F

T2 or T2g
T1 or T1g
A2 or A2g
d2, d7 tetrahedral

0

d2, d7 octahedral

d3, d8 octahedral
d3, d8 tetrahedral
Ligand field strength (Dq)

d2

3F, 3P, 1G, 1D, 1S

Real complexes

13

Tanabe-Sugano diagrams

d2

Electronic transitions and spectra

14

Other configurations
d3
d9

d1

d2

d8

Other configurations

d3

The limit between
high spin and low spin

15

Determining Δo from spectra

d1

d9

One transition allowed of energy Δo

Determining Δo from spectra
mixing

mixing

Lowest energy transition = Δo

16

Ground state mixing

E (T1g→A2g) - E (T1g→T2g) = Δo

The d5 case

All possible transitions forbidden
Very weak signals, faint color

17

Some examples of spectra

Charge transfer spectra
Metal character

LMCT
Ligand character

Ligand character

MLCT
Metal character
Much more intense bands

18



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