REVERSIBLE FORMATION OF BINUCLEAR COMPLEXES BETWEEN E-2-CARBOXYLATO(TETRAETHYLENEPENTAMINE)COBALT(III) AND NICKEL(II) COBALT(II) IN AQUEOUS-SOLUTION - ANOMALOUS BEHAVIOR IN THE DISSOCIATION OF BINUCLEAR COMPLEXES/

The kinetics of the reversible formation of binuclear species between M(OH2)(6)(2+) (M = Ni-II and Co-II) and oxygen-bonded (tetren)Co(pycH) (3+) (tetren = tetraethylenepentamine, pycH = N-protonated pyridine-2- carboxylate) have been investigated by stopped-flow spectrophotometry at 25 degrees C, I = 0.3 mol dm(-3). Both the protonated (pyridine-N) and deprotonated forms of the Co-III complex were involved in the form ation of the binuclear complex (tetren)Co(pyc)Co4+, whereas only the d eprotonated form of the complex was involved in the formation of (tetr en)Co(pyc)Ni4+ The rate date for the formation of the binuclear comple x are consistent with an I-d mechanism. Interestingly, the dissociatio n of the binuclear Co-II complex (tetren)Co(pyc)Co4+ was acid-catalyse d while that with Ni-II was acid-independent. A suitable explanation f or this anomalous behaviour has been discussed.