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

The kinetics of formation and dissociation reactions of [Ru(CN)(5)L](3-) wi th a series of heterocyclic ligands were studied in aqueous media. In this presence of an excess of heterocycle, the observed second order rate consta nts were calculated from the k(obs) versus [ligand] plot at mu = 0.100 m Na ClO4. Activation parameters for the formation reactions (Delta H double dag ger = 28 +/- 7 kJ mol(-1) and Delta S double dagger = 140 +/- 35 J K-1 mol( -1)) are comparable for all systems, indicating a common mechanism. The kin etics of exchange of coordinated heterocycles for 1,3,5-triazine yielded a rate saturation typical of a limiting dissociative mechanism. Activation pa rameters of the limiting first order specific rate of dissociation reaction s were Delta H double dagger = 85 +/- 7 kJ mol(-1) and Delta S double dagge r =18 +/- 4 J K-1 mol(-1). Equilibrium constants were calculated from the s econd order rates of formation and pseudo-first order rates of dissociation reaction.