Mechanistic Disparity in the Electron Transfer Reactions of Thiosulfate with Di-mu-oxo-bis(1,4,8,11-tetraazacyclotetradecane)-dimanganese(III,IV)and Di-mu-OXO-bis(1,4,7,10-tetraazacyclododecane)-dimanganese(III,IV)Complexes

摘要

A comparative kinetic study of the reactions of two mixed valence manganess(III,IV)complexes of macrocyclic ligands'.[L~1 Mn~IV(O)_2Mn~III L~1],1(L~1=1,4,8,11-tetraazacyclotetradecane)and [L~2Mn~IV(O)_2Mn~III L~2],2(L~2=1,4,7,10-tetraazacyclododecane)with thiosulfate has been carried out by spectrophotometry in aqueous buffer at 30 deg C Reaction between complex 1 and thiosulfate follows a first-order rate saturation kinetics.The pH dependency and kinetic evidences suggest the participation of two complex species of Mn~III(mu-O)_2 Mn~IV under the experimental conditions.Detailed kinetic study shows that reduction of 2 proceeds through an autocatalytic path where the intermediate(Mn~III)_2 species has been assumed to catalyze the reaction.The difference in the reaction mechanisms is ascribed to the difference in stability of the intermediate complex species,the evidence for which comes from the electrochemical behavior of the complexes and time dependent EPR spectroscopic measurements during the reduction of 2.