Chem 341
Coordination Chemistry – Electronic Spectra
Chapter 11: pp 419-421, 428-429, 437-438
HW: 12 (assume o is lowest energy transition), 15, 16, 17, 18,
21, 24, 25, 27,
Goals: Predict relative intensities of electronic transitions;
distinguish dd, LMCT and MLCT; Distinguish excited states
Upcoming:
11/18, 11/21: Ch. 11. Electronic transitions in metal complexes
11/23 no class
11/28, 11/30: Acc. Chem. Res. 2003, 36, 876-887
Photochemistry for solar energy
12/2: Exam III
UMass Amherst

Created by Karsten Theis
Selection Rules for electronic transitions
 1. Laporte selection
 2. Spin selection
 How to relax these rules?
• How to get rid of g symmetry?
• Spin-orbit coupling ‘mixes’ spin states to relax rule 2
        ...   
2
        ...   
3
Why 2 peaks in the UV-Vis spectra of V(OH2)63+
A) the two electrons undergo transitions at different E due
to ground-state Jahn-Teller distortion
B) one is spin –allowed, the other is spin-forbidden
C) ligand-to-metal charge transfers
D) two different excited states (d-d)
E) metal-to-ligand charge transfer
        ...   
4
Why 2 peaks in the UV-Vis spectra of V(OH2)63+
3T
1g
3T2g and 3T1g  3T1g
Only 1e- moves at a time!
Excited states have same spin multiplicity as ground state.
Jahn-Teller distortion is weak here. Much stronger when
eg* populated.
        ...   
5
        ...   
6
Calculate CFSE for hexa-aquo(Cr3+)
A) 7,000 cm-1
B) 17,000 cm-1
C) 24,000 cm-1
D) 50,000 cm-1
E) 650 nm
What color is Cr(OH2)63+?
        ...   
7
Calculate CFSE for hexa-aquo(Cr3+)
D) 50,000 cm-1
What color is Cr(OH2)63+? Greenish
Absorbs orange and violet
        ...   
8
M(OH2)62+
 Which peaks are spinforbidden?
 A) 1 only
 B) 2 only
 C) 1 and 2
 D) 1, 2, 3
 E) 4
1
3
2
4
9
        ...   
M(OH2)62+
 Which peaks are spinforbidden?
 C) 1 and 2
1
3
2
4
        ...   
10