KINETICS AND MECHANISM OF AQUA LIGAND SUBSTITUTION-REACTIONS FROM CIS-DIAQUA-BIS(BIPYRIDINE)RUTHENIUM(II) ION BY PYRIDINE-2-ALDOXIME IN AQUEOUS-MEDIUM

The kinetic behaviour of cis-[Ru(bipy)2(H2O)2]2+ towards the anating l igand pyridine-2-aldoxime as a function of temperature, ligand concent ration, substrate complex concentration and pH is reported and the rat e expression Rate = k1k2[Ru(bipy)2(H2O)2]2+ [LL]/(k-1 + k2[LL]) is est ablished where k1 is the water dissociation rate constant for the slow step, k-1 is the rate constant for the aquation, k2 is the ligand-cap turing rate constant of the five-coordinate intermediate [Ru(bipy)2(H2 O)]2+ and LL is pyridine-2-aldoxime. The reaction is pH-dependent in t he pH range 3.65-5.50. The enthalpy and entropy of activation were obt ained using Eyring plots. The results are in conformity with a dissoci ative mechanism.