Complexation of cobalt(II) with histidinato(pentaammine)cobalt(III) in aqueous medium. A kinetic and mechanistic study |
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Authors: | Nigamananda Das Rita Das |
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Affiliation: | (1) Regional Research Laboratory, Bhubaneswar 751 013 Orissa, India;(2) Department of Chemistry, MPC College, Baripada 757001 Orissa, India |
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Abstract: | Summary The kinetics of formation and dissociation of the binuclear complex of CoII with histidinato(pentaammine)CoIII have been studied at 10.0°Ct°C25°C and I = 0.3 mol dm–3 (ClOinf4sup–). The formation of the binuclear complex, [(NH3)5CoIIILCoII]4+ (L = histidinate), in the 5.7–6.8 pH range involves the reaction of Co(OH2)inf6sup2+with the deprotonated, (NH3)5CoL2+, and monoprotonated, (NH3)5CoLH3+, forms of the complex. The rate and activation parameters for the formation are consistent with an Id mechanism. The binuclear species undergoes dissociation to yield the parent CoIII substrate and Co(OH2)inf6sup2+via spontaneous and acid-catalysed paths. Comparison of spontaneous dissociation rate of the binuclear complex with other related systems indicated the chelate nature of the binuclear species. |
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