One electron oxidation of Ni(II)-iminodiacetate by carbonate radical

Abstract

Reactions of carbonate radical (CO3−), generated by photolysis or by radiolysis of a carbonate solution with nickel(II)-iminodiacetate (Ni(II)IDA) were studied at pH 10.5 and ionic strength (I)==0.2 mol·dm−3. The stable product arising from the ligand degradation in the complex is mainly glyxalic acid. Time-resolved spectroscopy and transient kinetics were studied using flash photolysis. From the kinetic data it was suggested that the carbonate radical initially reacts with Ni(III)IDA with a rate constant (2.4±0.4)·106 dm3·mol−1·s−1 to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7·102·s−1) to give a radical intermediate of the type Ni(II)RNHCHCO 2 − ) which rapidly forms an adduct containing a Ni−C bond. This adduct decays very slowly to give rise to glyoxalic acid. From a consideration of equilibrium between Ni(II)IDA and Ni(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni(II)IDA couple was determined to be 1.467 V.