Formation and properties of the trivalent nickel-ethylene diamine tetra-acetic acid (EDTA) complex in aqueous solutions: A pulse-radiolytic study

Ni(II) EDTA is oxidized by OH radicals to an unstable Ni(III) EDTA complex with a rate of 2·3×10⁹dm³mol^-1s^-1. The trivalent complexformed undergoes a rearrangement reaction to a relatively stable form of Ni(III) EDTA with a rate constant of 2·0×10³s^-1. The spectra of both forms of Ni(III) EDTA have maxima at 288 nm. Ni(III) EDTA reacts with O₂ and I^- with rates k = 6·5×10² dm³ mol^-1 s^-1 and 1·25×10³ dm³ mol^-1 s^-1, respectively, The redox potential of the couple Ni(II) EDTA/Ni(III) EDTA is estimated as 0·54≤E⁰≤1·06 V. The mechanisms of the reactions involved are discussed.