1. 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

2. d1  d6 d4  d9
Orgel diagram for d1, d4, d6, d9
Energy T2 E
d1, d6 tetrahedral Eg
T2g
d1, d6 octahedral
d4, d9 tetrahedral
or T2
or E
T2g or
Eg or
d4, d9 octahedral D D D
ligand field strength

3. [Ti(OH2)6]3+ d1 oct 2Eg 2Eg  2T2g 2D 2T2g - D A E LF strength
n / cm-1 -
30 000
20 000
10 000
2Eg
2Eg  2T2g 2D
2T2g E
LF strength
Orgel diagram for d1, d4, d6, d9 D
d4, d9 tetrahedral
T2g or T2
d4, d9 octahedral
Eg or E
d1, d6 tetrahedral
d1, d6 octahedral

4. ? P T2(g) and E(g) D F Effect of a ligand field on Ground State TermsGS
d1 d9 2D
d2 d8 3F 3P
d3 d7 4F 4P
d4 d6 5D
d5 6S
free ion
ligand field D
T2(g) and E(g) P F ?

5. Octahedral d2 complex
d2  d7
3P: high repulsion
In a LF, these orbitals are unaffected
xz + z2
yz + z2
xy + x2-y2
3T1g
3F: low repulsion
In a LF, orbitals in the t2g set go down in energy, orbitals in the eg set go up in energy
3A2g
eg eg singly degenerate, high energy
x2-y2 + z2
x2-y2 + yz
x2-y2 + xz
xy + z2
xy + xz
xy + yz
xz + yz
3T2g
eg t2g triply degenerate, medium energy
3T1g
t2g t2g triply degenerate, low energy

6. Octahedral d3 complex
(same terms, different spin)
d3  d8
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 
4T1g
4T2g
4A2g

7. Ligand field strength (Dq)
Orgel diagram for d2, d3, d7, d8 ions
Quantum Mixing
Energy
A2 or A2g
T1 or T1g
T2 or T2g
T1 or T1g P F
d2, d7 tetrahedral d2, d7 octahedral
d3, d8 octahedral d3, d8 tetrahedral
Ligand field strength (Dq)

8. Energy level diagram for oct d2, d7, tet d3, d8
15 B'
15 B
15 B > 15 B'
10 Dq
6 Dq
2 Dq
T1(g)
A2(g)
T2(g) x
A2(g)
T2(g)
T1(g) P F
10 Dq
6 Dq
2 Dq

9. Calculating B' and x d7 octahedral complex n1 n2 n3 n1 n2 n3
[Co(H2O)6]2+ n1 n2 n3
4T1g n1 n2 n3
n1 = cm-1
n2 = cm-1
n3 = cm-1 A
10 Dq
6 Dq
2 Dq x
15 B'
4A2g
v / cm-1
25 000
20 000
15 000
10 000
4T2g
4T1g

10. Ligand field strength (Dq)
Orgel diagram for d2, d3, d7, d8 ions
Energy
A2 or A2g
T1 or T1g
T2 or T2g
T1 or T1g P F
d2, d7 tetrahedral d2, d7 octahedral
d3, d8 octahedral d3, d8 tetrahedral
Ligand field strength (Dq)

11. Energy level diagram for oct d2, d7, tet d3, d8
n1: x + 8 Dq
n2: 2 x + 6 Dq + 15 B'
n3: x + 18 Dq
A2(g) n1 n2 n3
n1: T2(g)  T1(g)
n2: T1(g)(P)  T1(g)
n3: A2(g)  T1(g)
T1(g)
10 Dq x P
15 B
15 B'
T2(g)
2 Dq F
6 Dq
T1(g) x