Crystal-Field Theory Ligand-Field or Molecular Orbital Theory

X2+y2+z2
2z2-x2-y2, x2-y2

xy, xz, yz

x, y, z,

Molecular Orbital Theory – Octahedral complexes









X2+y2+z2
2z2-x2-y2, x2-y2

xy, xz, yz

x, y, z,

16S [Ne] 3s23p4

M – L σ - bonding in a [ML6]n+ complex

M-L only σ bonding Bonding Example:[ Mo(CO)6]
Model Mo: 5s1 4d5 – 6e-
6CO: 12 e-
[CoF6]3- High Total of 18 e- fill into MOs:
Spin (HS) a1g2, t1u6, eg4, t2g6 Low Spin (LS)
Co3+ : d6 – 6e-
6F-: 6x2 - 12e- so far not so different
Total: 18 e- from CFT as far as
t2g & eg
a1g2, t1u6, eg4, t2g4 eg*2
orbital splitting, filling
in [ML6]n+

Considering M-L π Bonding
difference between CFT and LFT

dπ-pπ dπ -dπ

dπ-pπ* dπ-σ*

Consider t2g set of ligand π-orbitals for Oh complex along x and z directions
z interacting with dxz M orbital

px and pz LGO π-interaction wirh dxz
bonding and antibonding

x

Effect of π bonding with π-donating ligands: e.g., F-, Br-, Cl-, I-

electrons from π-donor L
fill t2g π orbitals

electrons from M fill t2g*
hence

∆O < no π-bonding