Nickel(III)–tris(di-imine) complexes: a series of strong one-electron oxidants
The complexes [Ni(III)(LL)3](ClO4)3 (LL = phen, bipy, and substituted derivatives) have been isolated as products of the electrolysis in acetonitrile of the corresponding nickel(II) species. Electron spin resonance measurements for all nickel(III) species in frozen anhydrous CH3CN and in frozen 4.0 M HClO4 solutions (77 K) show a single near symmetric line shape (g ≈ 2.10) with fine structures appearing only in the presence of mixed solvent systems. In a CH3CN/5% H2O glass (77 K) quintets in the [Formula: see text] and [Formula: see text] regions are observed [Formula: see text]consistent with Jahn–Teller distortion expected for a low-spin d7 system. Ultraviolet–visible spectra are also reported. Electrode potentials for the Ni(LL)33+/2+ couples in CH3CN (0.1 M NaClO4) lie in the range 1.51 V (Ni(4,4′-Me2bipy)33+) to 1.82 V (Ni(5-NO2-phen)33+) and the powerful oxidizing nature of these species has been confirmed in reaction with both organic and inorganic substrates.