Substitution reactions at pentacyanoferrate(II) complexes: linear free-energy relationships in mixed solvents

Abstract

The kinetics of replacement of 4-phenylpyridine (4-phpy) by cyanide in Fe(CN)₅(4-phpy)^3– have been studied in various isodielectric water–cosolvent mixtures at 298 K. The experimental data are well correlated through the following equation: δΔG^#_exp=aδA_m+bδB_m+cG^exc where A_m, B_m and G^exc are the acidity parameter, the basicity parameter and the excess Gibbs free energy of the mixture, respectively. This multiparameter regression was also applied to data, taken from the literature, of substitution reactions at different pentacyanoferrate(II) complexes in order to show its general validity for explaining the effect of the medium on these types of processes in binary aqueous mixtures.