A New Suit - Ligand-centred Reactions

The thermodynamic stability of a complex can be expressed in terms of a stability constant, which reports the ratio of complexed ligand to free metal and ligand in an equilibrium situation. 

For complexation of a set of ligands, each successive addition has a stability constant (Kn) associated with it, with each successive stability constant progressively smaller for a fixed stereochemistry. An overall stability constant ((3n = Ki K2-.. . -Ain) expresses the stability of the completed assembly. 

Whereas thermodynamic stability is concerned with complex stability at equilibrium, kinetic stability is concerned with the rate of formation of a complex leading to equilibrium. Complexes undergoing reactions rapidly are labile, those reacting slowly are inert. 

Reactions of complexes may involve changes to the coordination sphere, the metal oxidation state and/or the ligands themselves. Partial or complete ligand replacement (substitution) is the most common reaction met in metal complexes. 

Mechanisms for optical and geometrical isomerization reactions similar to those employed for substitution reactions can be envisaged. Additionally possible is a twist mechanism, involving distortion of the polyhedral framework in the activated state but in which no ligands depart or join the coordination sphere. 

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