Rates of Ligand Substitution

What are inert complexes

Complexes that are thermodynamically unstable but survive for long periods (at least a minute) are called inert 

What are labile complexes

Complexes that undergo more rapid equilibration are called labile 

Describe how lower activation energy increases rate of reaction

• stabilisation of the transition state (TS) 

• destabilisation of the ground state 

How does oxidation state affect rate

• Oxidation state of the metal will affect rate.

• Rates are slower for ions with higher charge

• Due to the fact that

  • metal ligand bonds are harder to break

  • there is less space for attack by the incoming ligand

Give the dissociative and associative reactions for metal ligands

Detail how distribution of 3d electrons effects rate

d⁰ → d³ : rates drop

• Metal ion nuclear charge increases. SN1 becomes harder. Since the electrons go into the orbitals pointing in between the ligands, Z_eff felt by the ligands increases and the M-L bonds get stronger.

• SN2 gets harder as well. The electrons in d_xy, d_xz, d_yz protect the metal from an attack by an incoming ligand.

d³ → d⁵ : rates rise

• SN1 easier, The 4th and 5th electron go into the orbitals pointing at the ligands. This makes the M-L bonds weaker.

• SN2 easier, gets easier as well since the electrons don’t protect from attack.

d⁵ → d⁸ : rates drop

• The electrons go into the orbitals lying in between the ligands

d⁸ → d¹⁰ : rates rise

• The electrons go into the orbitals pointing at the ligands