Interaction of bivalent transition metal ions with iminodiacetato-(pentaammine/tetraammine)cobalt(III) ions. A kinetic and equilibrium study

Abstract

The kinetics of reversible complexation of Ni lI and Co Il with iminodiacetato(pentaammine)cobalt(III), [(NH3) 5-Co(idaH2)] 3+ and Ni II with iminodiacetato(tetraammine)-cobalt(III), [(NH3)4Co(idaH)] 2 +, have been investigated by the stopped-flow technique at 25 ~ pH = 5.7-6.9 and I = 0.3 tool dm-3. The reaction paths (NH3)sCo(idaH) z + + M 2 + ,~-(NH3)sCo(ida)M 3 + + H + (NH3)sCo(ida) + + M z + ~(NH3)sCo(ida)M 3 + (NH3)4Co(ida) + + Ni 2 + ,-~-(NH3)4Co(ida)Ni 3 + have been identified (idaH = N+Hz(CH/CO2)2H, ida = NH(CHzCOO) 2-]. The rate parameters for the formation and dissociation of the binuclear species are reported. The data are essentially consistent with an I d mechanism.The dissociation rate constants of the binuclear species indicate that Ni / + and Co 2 + are chelated by the coordinated iminodiacetate moiety.