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-II and Co-II with iminodiacetato(pentaammine)cobalt(III), [(NH3)(5)Co(idaH(2))](3+) and Ni-II with iminodiacetato(tetraammine)-cobalt(III), [(NH3)(4)Co(idaH)](2+), have been investigated by the stopped-flow technique at 25 degrees C, pH = 5.7-6.9 and I = 0.3 mol dm(-3). The reaction paths (NH3)(5)Co(idaH)(2+) + M(2+) reversible arrow (NH3)(5)CO(ida)M(3+) + H+ (NH3)(5)Co(ida)(+) + M(2+) reversible arrow (NH3)(5)Co(ida)M(3+) (NH3)(4)Co(ida)(+) + Ni2+ reversible arrow (NH3)(4)Co(ida)(Ni3+) have been identified (idaH = N+H2(CH2CO2)(2)H, ida = NH(CH2COO)(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 Ni2+ and Co2+ are chelated by the coordinated iminodiacetate moiety.