Abstract Nickel(II) complexes with tridentate oxime chelate HRR′Y system in alkaline media are oxidized by ammonium persulfate to produce red-violet crystals of Ni(HRR′Y)-(RR′Y)(ClO4)2 which (i) oxidize iron(II) to iron(III), (ii) have μeff≃2.0 B.M., (iii) exhibit characteristic polycrystalline epr spectra of S = 1/2 in the axial field (g∥ = 2.04, g⊥ = 2.16) and also are oxidized by concentrated nitric acid to yield dark-violet diamagnetic nickel(IV) species Ni(RR′Y)2(ClO4)2. Cyclic voltammetry (CV) of Ni(RR′Y)2(ClO4)2 has been thoroughly done in well-buffered media over a wide range of pH values. Below pH 6.0, CV data show a single, reversible, two-electron, two-proton transfer process followed by an irreversible chemical decomposition of the nickel(II) species. In the pH range 7.00 – 9.00 two distinct reversible, one-electron processes are observed corresponding to Ni(IV) – Ni(III) and Ni(III) – Ni(II) couples. The first of these has no Proton involvement while the other is proton dependent. The E0′ 298 values for the various couples have been accurately determined from CV data.