This document discusses the kinetic stability of metal complexes through dissociative and associative reaction mechanisms. Inner orbital complexes with d2sp3 hybridization form shorter, stronger metal-ligand bonds and are always inert. Outer orbital complexes with sp3d2 hybridization form larger, weaker bonds and can be either labile or inert depending on the mechanism. For the associative mechanism, complexes with low-lying unhybridized d-orbitals can be either inert or labile depending on whether the d-orbitals are occupied or vacant. The lability is determined by calculating the change in crystal field stabilization energy between the transition state and original complex.

1. Thermodynamic and kinetic stability
of metal complexes, Part 2, Kinetic
stability

2. Kinetic
stability
Labile
complexes
Inert
complexes

5. Reaction through dissociative mechanism
Outer orbital complexes
sp3d2 hybridization, larger and weaker M-L bonds (higher
energy)
Inner orbital complexes
d2sp3 hybridization, shorter and stronger M-L bonds (lower
energy)
Inner orbital complexes: Inert always
Outer orbital complexes: Labile always

6. Reaction through associative mechanism
Outer orbital and inner orbital complexes with low lying
unhybridized metal d-orbitals.
These orbitals are center attack by the incoming ligand in
associated mechanism of substitution.
Inert complexes
Electrons are present in the unhybridized d-orbitals.
Labile complexes
Vacant unhybridized d-orbitals.
[MnCl6]3- = Labile
[Cr(CN)6]3- = Inert
d2sp3
XX XX XX XX XX XX
XX XX XX XX XX XX
sp3d2

7. Inner orbital complexes

10. 6 4
)
6 3
in eg

11. Dissociative mechanism: Square pyramidal intermediate
Loss in CFSE = CFSE of SP – CFSE of Oh
Associate mechanism: Pentagonal bipyramidal transition state
Loss in CFSE = CFSE of PBP – CFSE of Oh
If the loss in CFSE negative = inert complex
If the loss in CFSE positive or zero = labile complex
Basolo and Pearson calculated CFSE for LS and HS square
pyramidal and pentagonal bipyramidal complexes.