Electron transfer reactions of tris(polypyridine)cobalt(in) complexes, Co(N-N)₃]³⁺, with verdazyl radicals in acetonitrile solution

The kinetics and mechanisms of the reactions of 3-(4-X)-phenyl-1,5-diphenyl-verdazyl radicals where X = Cl, H, CH₃ and CH₃O with [Co(N-N)₃]³⁺, N-N = 2,2′-bipyridyl (bpy), 1,10-phenanthroline (phen) and 4,7-dimethyl-1,10-phenanthroline (4,7-Me₂phen), have been investigated in acetonitrile at 25°C and ionic strength 0.05 mo) dm ^-3 ("C₄H₉)₄NPF₆ using stopped flow spectrophotometry. In all cases, transfer of one electron from the radical takes place resulting in the production of a Co(II) species and a verdazylium cation. The electron transfer occurs by an outer-sphere mechanism and the reactions appear to be consistent with Marcus theory. The self-exchange rate constants for the verdazyl-verdazylium cation have been estimated and are of the order of 3.4(± 1.9) × 10⁷ dm³ mol^-1 s^-1. This rate constant is consistent with the fact that the reactions of [Ru(bpy)₃] ³⁺ with verdazyl radicals are too rapid to be investigated by stopped flow spectrophotometry.