ONE-ELECTRON OXIDATION OF NI(II)-IMINODIACETATE BY CARBONATE RADICAL

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 co mplex is mainly glyoxalic acid. Time-resolved spectroscopy and transie nt 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). 10(6) dm(3) . mol(-1). s(- 1) to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7 . 10(2) . s(-1)) to give a radical intermediate of the type Ni(II)RNHCHCO(2)(-)) which rapidly forms an adduct contai ning a Ni-C bond. This adduct decays very slowly to give rise to glyox alic acid. From a consideration of equilibrium between NI(II)IDA and N i(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni( II)IDA couple was determined to be 1.467 V.