Formation of cobalt (ɪɪɪ) polyaminopolycarboxylate complexes in aqueous solutions by the peroxide oxidation of the cobalt (ɪɪ) complexes

The dynamics of the formation of cobalt(iii) complexes with anions of iminodiacetic, nitrilotriacetic, ethylenediaminetetraacetic, and diethylenetriaminepentaacetic acids in aqueous solutions by the peroxide oxidation of cobalt(ii) polyaminopolycarboxylates was studied by spectrophotometry and potentiometry. The optimum conditions for the formation of coordination cobalt particles in the highly oxidized state were selected, and the composition of the formed cobalt(iii) chelates was determined. Data on the thermodynamic stability of the coordinatively bound cobalt particles, specific features of the kinetics of peroxide oxidation, and the influence of the concentrations of the main components and acidity of the solutions on the rate of redox processes of cobalt(iii) polyaminopolycarboxylate formation were obtained. It was found that a strong catalytic decomposition of the reagent-oxidant at pH > 4.0 occurs during the formation of oxygenated intermediates in solutions of mononuclear ethylenediaminetetraacetate and binuclear diethylenetriamine-pentaacetate complexes of cobalt(ii). Based on the NMR spectroscopy data, a mechanism for the formation of the oxygenated particles was proposed. It was shown that diamagnetic binuclear oxygenated chelates of cobalt(iii) are characterized by low kinetic stability, which leads to the deoxygenation and formation of weakly paramagnetic mononuclear complexes of cobalt(iii).