Kinetics of aquation of tris(5-nitro-1,10-phenanthroline)iron(II) in acetone–water and in t-butyl alcohol–water mixtures: endostatic analysis of activation parameters

Abstract

Rate constants and derived thermodynamic activation parameters are reported for the aquation of [Fe(5NO₂-phen)₃]²⁺ in acetone–water and in t-butyl alcohol–water mixtures. The data have been analysed to obtain kinetic activation parameters for reaction in corresponding mixtures where the ratio of activities of the two solvent components is constant, i.e. under endostatic conditions. A method is described for calculating endostatic activation parameters from kinetic data and molar thermodynamic excess functions for the binary mixture. The results of these calculations are discussed in the light of the known properties and structures of the solvent mixtures. The solvent dependence of the activation Gibbs function, ΔG_α^‡. calculated under endostatic conditions for the aquation of the iron complex, reflects changes in solvent structure more markedly than the conventional activation parameter ΔG^‡ calculated directly from the rate constant using transition-state theory. This trend has been previously reported for the hydrolysis of 2-chloro-2-methylpropane, thereby indicating that the mechanisms of aquation for both reactants are similar, ie. dissociative.