The chelate effect: a simple quantitative approach

Abstract

Equations are constructed which accurately predict the stability constants of metal complexes of polydentate ligands from the stability constants of the complexes of the unidentate analogues. The factors considered are the asymmetry of the standard state, and the reduction of steric hindrance and mutual electrostatic repulsion in the complexes of the polydentate as compared with the unidantate ligands. The equations have been applied succassfully to complexes of polyamine ligands and of ligands containing alkylamine and carboxylate functional groups. The same equations can be used to calculate formation constants of complexes containing unidentate ligands which are unstable in aqueous solution from the stability constants of stable complexes of polydentate ligands. Thus, logK₁ 4.3 has been calculated for the complex [Fe(NH₃)]³⁺.