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 complex is mainly glyoxalic 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)RNHCHCO2-) 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.