Studies in nickel(IV) chemistry. Part 3. Kinetics of metal(II) ionmediated acid decomposition of tris(dimethylglyoximato)nickelate(IV) in aqueous medium

Abstract

The kinetics of metal(II) ion-mediated acid decomposition of tris(dimethylglyoximato)nickelate(IV), [Ni(dmg)₃]^2–, with concomitant intramolecular electron transfer to produce [M(Hdmg)₂] and Ni²⁺(aq) have been studied at 35 °C and ionic strength 0.57 mol dm^–3 in aqueous medium in the range 3.6 ≲ pH ≲ 6.8. The reactions proceed via equilibrium formation of 1 : 1 adducts involving the protonated Ni^IV complex and M^II(aq)(M = Cu, Zn, or Ni) present in the medium. While the rate-determining steps in the reactions with Cu^II are envisaged to involve acid decomposition of the adduct formed in addition to proton-assisted decomposition of the Ni^IV complex, those in the reactions with Zn^II and Ni^II proceed essentially by routes parallel to the proton-assisted decomposition. U.v.–visible spectral changes in the Ni^IV–Cu^II reaction indicate the formation of the 1 : 1 adduct.