Single vs double bridging in inner-sphere electron transfer reactions

Abstract

Stabilities of polynuclear complexes {[(en) 2Cr III(OH) 2] n M II} ( n+ 2)+ , where n = 1, 2; M II = Mn, Fe, Co, Ni, Cu, Zn, and kinetics of electron transfer between cis-[(en) 2Cr(OH 2) 2] 3+ and Cr 2+ in aqueous solution are reported. The data for this and for the analogous cobalt(III) systems are used to calculate upper limits for the rates of intramolecular electron transfer in the double-bridged binuclear mixed-valence ions [(en) 2M III(OH) 2Cr II(aq)] 3+. In at least one of the two cases, namely M III = Cr III, the rate is less than that in the single-bridged ion [(H 2O)(en) 2M III(OH)Cr II(aq)] 3+.