ELECTRON TRANSFER REACTIONS OF THIOSULFATE ION AND DIAQUOTETRAKIS (2,2’- BIPYRIDINE) - µ - OXODIRUTHENIUM(III) ION IN AQUEOUS PERCHLORIC ACID

Kinetics and mechanism of the electron transfer reactions of thiosulfate ions and diaquotetrakis (2,2’- bipyridine) - µ - oxodiruthenium(III) ion, [(H2O)2(bpy)4Ru2O]4+, has been studied in perchloric acid at a temperature, T = 31.0 ± 1°C, ionic strength, I = 0.5 mol dm-3 (NaClO4) and hydrogen ion concentration, [H+] = 5.0 x 10–2 mol dm-3. The reaction showed a stoichiometry of 1:2 ([(H2O)2(bpy)4Ru2O]4+: S2O32–), first order dependence with respect to [(H2O)2(bpy)4Ru2O]4+] and [S2O32–], second order overall. Increase in [H+] affected the rate of reaction directly while increase of the ionic strength affected the rates of the reaction adversely. The rate equation for the reaction has been proposed as: –d[[(H2O)2Ru2O4+]/ dt = (a+b[H+])[[(H2O)2Ru2O4+][S2O32–].Added anions and cations altered the rates of the reaction. Based on the lack of evidence of the formation of intermediate complex (from absence of intercept in the Michaelis-Menten plot and lack of shift in λmax of the reaction mixture 1 minute after start of reaction from that of the dimer) and observable added ion catalysis, it is proposed that the reaction most probably proceeded through the outer sphere mechanism. A plausible mechanism is proposed.