Kinetics and mechanism of mercury catalysed ligand exchange reaction between hexacyanoferrate(II) and phenanthroline in aqueous medium

Abstract

Kinetic and mechanistic studies of Hg(II)-catalysed exchange of co-ordinated cyanide in hexacyanoferrate(II) by phenanthroline (Phen) were performed by following the appearance of the coloured complex [Fe(CN)4 Phen]3– at 528 nm, temperature = 25 ± 0.10 0C, pH = 3.0 ± 0.02. The effects of pH, [Fe(CN)6]4– and [Phen] concentrations on the reaction rate have been studied and explained. The rate shows variable order dependence on [Fe(CN)6]4–. The effects of dielectric constant, water content, temperature and ionic strength of the medium on the reaction rates have been used to visualise the formation of a polar activated complex and suggest an interchange dissociative mechanism for the catalysed reaction. The varying catalytic activity of Hg(II) as a function of concentration has also been studied and explained in detail. Activation parameters of both catalysed and uncatalysed reactions has were derived and supported the proposed mechanistic scheme.