1001-1004The kinetics of reversible formation of binuclear complex between histidinatopentaarnminecobalttlll) and Ni(ll) has been investigated at 20-40°C, I = 0.3 mol dm-3,[Ni(II)]= 0.01-0.05 mol dm-3 and pH= 5.65 to 6.84. The formation of the binuclear species occurs via [H+] independent and [H+]-1 dependent paths, the latter arising out of protonation preequilibrium of the pendant amine function of the histidine moiety bound to cobalt(III) by the carboxylate group. The dissociation of the binuclear species is pH independent in the range studied. The rate and activation parameters for the formation and dissociation of the binuclear species are reported. The rate limiting step in the formation of the binuclear species is the rate of water dissociation from Ni(OH2). The results are consistent with chelation of Ni(ll) by the tertiary nitrogen and primary amine group of histidine moiety
