Analysis of water molecules exchange mechanism in 3d cation aquacomplex

Abstract

The ligand exchange rate is the significant part of complex compound kinetic. The mechanism of this process may be different. In the article the ability to apply the quantum-chemical method for determination of intermediates type and ligand exchange mechanism have been estimated. Our calculations have shown that the dissociative mechanism of water molecules exchange dominates for the majority of divalent 3d-cations aquacomplexes. It was found that rate of ligand exchange is inversely proportional to the energy logarithm of five intermediate ligand formative as associative mechanisms possible only for Ti²⁺ aquacomplexes. The associative mechanism is to be place for trivalent cations Ti³⁺, V³⁺, Mn³⁺ and Fe³⁺ aquacomplexes. Associative compounds of Cr³⁺ and Co³⁺ is forbidden and exchange of inner water molecules implement through the complex for such cations dissociative mechanism. This method allow to determine the ligand exchange rate in the complexes which haven’t these values and to estimate the labilite of the short-lived intermediate complexes.