Kinetic and mechanistic analysis of ligand substitution of aquapentacyanoruthenate(II) in SDS medium by 4,4′bipyridine

Substitution of coordinated water molecule from the coordination sphere of [Ru(CN)5H2O]3− with nitrogen donor ligand 4,4′Bipyridine (BipY) was studied in anionic micellar medium under pseudo first order condition as a function of ionic strength, pH, reactants concentration and temperature at 390 nm λmax of orange colored product [Ru(CN)4BipY]2−. The reaction was independent of [Ru(CN)5H2O]3− while it exhibited first order kinetics in [BipY] in the selected concentration range. The variation in ionic strength had negative effect on substitution rate. The surfactant SDS has negative charge similar to that of the complex [Ru(CN)5H2O]3−, therefore does not show any significant effect on the reaction rate except at concentration higher than critical micelle concentration. A suitable mechanism involving the ion pair dissociation of complex [Ru(CN)5H2O]3− and ligand BipY has been proposed. The activation parameters ΔH≠, ΔS≠ and Ea with respect to the slowest step of the mechanism were computed which supports the proposed mechanistic scheme.