Studies in nickel(IV) chemistry. Part 4. Kinetics of the electron transfer from L-ascorbic acid to tris(dimethylglyoximato)nickelate(IV) in aqueous medium

The kinetics of electron transfer from L-ascorbic acid (H2A) to tris(dimethylglyoximato)nickelate(IV), [Ni(dmg)3]2–, follow a pseudo-first-order disappearance of the NiIVcomplex in aqueous medium at 35 °C and I= 0.25 mol dm–3. The pseudo-first-order rate constant (kobs.) conforms to kobs.=kad+kred, where kad refers to the pseudo-first-order rate constant for the independently determined proton-assisted decomposition of the NiIV complex and Kred, to that for the intermolecular reduction of NiIV by H2A. The rate constants for the proton-assisted decomposition range from 4.6 to 2.6 × 10–7 s–1(pH range 1.6–12.3) and those for the reduction reaction range from 5.1 × 102 to 8 dm3 mol–1 s–1(pH range 1.6–11.1). The results are interpreted in terms of a probable mechanism involving a rate-determining outer-sphere one-electron transfer from the reductant to the oxidant NiIVspecies present in the solution, followed by a subsequent and kineticaliy indistinguishable rapid reaction of the NiIII intermediate.