1. No category

Transition Metals, Compounds and Complexes
or
Electronic Spectroscopy of Transition Metal Complexes
Dr. E.R. Schofield
Lecture 3:
Interpretation of weak field spectra
Electronic spectra from Orgel diagrams
Orgel diagram for d2, d3, d7, d8 ions
d1  d6
d4  d9
Orgel diagram for d1, d4, d6, d9
Energy
Eg
or
E
T2g or T2
D
T2g or T2
Eg or E
D
d1, d6 tetrahedral
d4, d9 octahedral
0
d1, d6 octahedral
d4, d9 tetrahedral
ligand field strength
D
d1 oct
2E
g
[Ti(OH2)6]3+
A
2E
g
 2T2g
D
2D
2T
2g
10 000
20 000
30 000
n- / cm-1
Orgel diagram for d1, d4, d6, d9
E
Eg or E
T2g or T2
D
D
T2g or T2
Eg or E
D
d1, d6 tetrahedral
d4, d9 octahedral
0
LF strength
d1, d6 octahedral
d4, d9 tetrahedral
D
Effect of a ligand field on Ground State Terms
free ion
GS
d1
d9
2D
d2
d8
3F
3P
d3
d7
4F
4P
d4
d6
5D
d5
6S
P
D
F
ligand field
T2(g) ?
and E(g)
Octahedral d2 complex
3P:
d2  d7
high repulsion
xz + z2
yz + z2
xy + x2-y2
In a LF, these orbitals are unaffected
3F:
3T
1g
low repulsion
In a LF, orbitals in the t2g set go down in energy, orbitals in the eg set go up in energy
x2-y2 + z2
3A
2g
eg eg
singly degenerate, high energy
x2-y2 + yz
x2-y2 + xz
xy + z2
3T
2g
eg t2g
triply degenerate, medium energy
1g
t2g t2g
triply degenerate, low energy
xy + xz
xy + yz
xz + yz
3T
Octahedral d3 complex
(same terms, different spin)
4P:
high repulsion
In a LF, these orbitals are unaffected  4T1g
4F:
low repulsion
The order of energy levels is the opposite to that for a d2 ion 
4T
1g
4T
2g
4A
2g
d3  d8
Orgel diagram for d2, d3, d7, d8 ions
Quantum Mixing
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)
Energy level diagram for oct d2, d7, tet d3, d8
T1(g)
P
x
T1(g)
A2(g)
15 B > 15 B'
A2(g)
15 B
15 B'
10 Dq
10 Dq
T2(g)
F
T2(g)
2 Dq
2 Dq
6 Dq
6 Dq
T1(g)
T1(g)
x
Calculating B' and x
d7 octahedral complex
[Co(H2O)6]2+
n3
4T
1g
A
n3
x
n2
4A
2g
n1
n2
15 B'
10 Dq
4T
2g
v / cm-1
25 000
n1
20 000
15 000
2 Dq
6 Dq
n1 = 8 000 cm-1
n2 = 16 000 cm-1
x
4T
1g
n3 = 19 400 cm-1
10 000
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)
Energy level diagram for oct d2, d7, tet d3, d8
A2(g)
n3
n 1:
x + 8 Dq
n 2:
2 x + 6 Dq + 15 B'
n 3:
x + 18 Dq
T1(g)
n2
x 10 Dq
P
15 B
F
15 B'
T2(g)
n1
2 Dq
6 Dq
T1(g)
x
n 1:
T2(g)  T1(g)
n 2:
T1(g)(P)  T1(g)
n 3:
A2(g)  T1(g)