Cyclic voltammetric studies of dioxygenbridged dinuclear cobalt(III) complexes

Abstract

Cyclic voltammetric studies were carried out for dioxygen-bridged dinuclear cobalt(III) complexes using platinum electrodes at different values of pH and ionic strength. Reversible electrode reactions occur particularly for the dioxygen complexes [(phen)₂Co(μ-O₂,NH₂)Co(phen)₂] (ClO₄)₄2H₂O and [(bpy)₂Co(μ-O₂, NH₂)Co(bpy)₂] (ClO₄)₄H₂O with 1,10-phenanthroline (phen) and 2,2-bipyridine (bpy) as the non-bridging ligands. For complexes with ammonia (NH₃) ethylenediamine (en) as the terminal ligands, there is quasi-reversible electrode behaviour at pH < 3 due to protonation of the peroxo complexes which subsequently undergo equilibration with isomeric forms. Such behaviour is well-marked for the peroxo complex [(en)₂Co(μ-O₂ NH₂)Co(en)₂](NO₃)₃. The decaammine complex [(NH₃ 5Co(μ-O₂Co(NH₃)₅](NO₃)₅ shows only a cathodic peak due to intramolecular charge transfer decomposition in solution after reduction at the electrode. Diffusion coefficients for all the dioxygen complexes were determined from the plots ofI p vs.v ^1/2.