Solvent-exchange reactions of metal ions. Diagnosis of mechanisms in terms of the bond order of the activated complexes

Abstract

An intersecting-state model has been applied to calculate activated complex bond orders, n^≠, in water-exchange reactions of metal ions. Under the assumption that metal–water bond-breaking–bond-forming processes have a concerted nature and the bonds have a harmonic behaviour, n^≠ is found to vary continuously from 0.5 to 1.0. Reaction mechanisms, assessed in terms of n^≠ and ΔV^≠, reveal that solvent-exchange mechanisms present a continuum between n^≠= 0.5 and 1.0 and dissociative and associative extremes. The extreme cases are an outer-shell association process, A(n^≠= 0.5, ΔV^≠≪ 0), an inner-shell association A_i(n^≠≈ 1.0, ΔV⁺≪ 0) and an inner-shell dissociation, D_i(n^≠= 1.0, ΔV^≠≫ 0). For the normal dissociation of a water–metal bond, D, 0 [graphic omitted] n^≠ < 0.5. However, nonharmonic behaviour has to be employed to estimate n^≠. Correlations between different types of mechanism and electronic structure are established. Data in some non-aqueous solvents are briefly discussed.