Kinetics of formation, dissociation and equilibrium constants of pentacyanoaquoruthenate(II) with heterocycles

Abstract

The kinetics of formation and dissociation reactions of [Ru(CN)₅L]³⁻ with a series of heterocyclic ligands were studied in aqueous media. In this presence of an excess of heterocycle, the observed second order rate constants were calculated from the k_obs versus [ligand] plot at μ = 0.100 m NaClO₄. Activation parameters for the formation reactions (ΔH^‡ = 28 ± 7 kJ mol⁻¹ and ΔS^‡ = 140 ± 35 JK⁻¹mol⁻¹) are comparable for all systems, indicating a common mechanism. The kinetics of exchange of coordinated heterocycles for 1,3,5-triazine yielded a rate saturation typical of a limiting dissociative mechanism. Activation parameters of the limiting first order specific rate of dissociation reactions were ΔH^‡ = 85 ± 7 kJ mol⁻¹ and ΔS^‡ =18 ± 4 J K⁻¹mol⁻¹. Equilibrium constants were calculated from the second order rates of formation and pseudo-first order rates of dissociation reaction.