Kinetics and mechanism of replacement of water in aquapentacyano-ferrate(II) ion with a variety of entering ligands in ethylene glycol solvent

Abstract

The kinetics of replacement of water in [Fe(CN)₅(OH₂)]^3– with pyridine, 3-cyanopyridine, nicotinamide, 4-aminopyridine, and cyanide have been studied in ethylene glycol solvent containing 0.055 mol dm^–3 water at 25 °C. The rate law obeyed is –d[Fe(CN)₅(OH₂)^3–]/dt =k₂′[Y][Fe(CN)₅(OH₂)^3–]. With excess of entering ligand Y, k_oba(=k₂′[Y]) is practically independent of water concentration. Values of ΔH^‡ and ΔS^‡ for the replacement of water by Y in the aqua-complex are almost identical for water and ethylene glycol solvents, supporting the assertion that Y replaces water in both solvents. These results strongly support I_d the, mechanism and make the D mechanism very unlikely.