Kinetics and Oxidation of Di-Oxo-Bridged Manganese (III, IV) Complex of (2,2’ Bipyridine) by Thiocyanate Ion in Aqueous Acidic Medium

The kinetics and oxidation of di-oxo-bridged manganese (III, IV) complex of (2,2’ bipyridine by thiocyanate ion (SCN-) has been studied in aqueous acidic medium. The stoichiometric determination expresses a mole ratio of 1:3. Kinetics study was carried out under pseudo - first order condition and showed that the rate of reaction was first-order with respect to [(bipy)2MnIIIO2MnIV(bipy)2]3+ and [SCN-] respectively. The rate of the reaction was acid dependent as the rate of reaction increased with increase in acid concentration. It was found to decrease with increase in ionic strength, suggesting a negative salt effect. This implies that two opposite charges were in operation during the redox reaction. The addition of added cations and anions (Mg2+, Ni2+, CH3COO- and NO3-) increased the rate of reaction and Michaelis-Menten’s plot showed a zero intercept. Based on the results of the spectroscopic studies which indicated no shift from the maximum absorbance of 683 nm, kinetic evidence from Michaelis– Menten’s plot with zero intercept and interaction with added cations and anions, an outer–sphere mechanism has been proposed for the oxidation of di-oxo-bridged manganese (III, IV) complex of (2,2’ bipyridine) by SCN-.