Electrode modification from the electrolysis of [M(Bipyridine)₃](ClO₄) ₂ (M = Co^II, Fe^II, and Ru^II) in media of low dielectric constant. Electrocatalytic behavior and an amperometric C₆₀ sensor

The voltammetric behavior of transition metal complexes of 2,2′-bipyridine, [M^II(bpy)₃](ClO₄)₂ (M^II = Co^II, Fe^II, or Ru^II, in toluene/acetonitrile mixtures has been studied by cyclic voltammetry. In solutions with a low acetonitrile-to-toluene ratio and tetra(n-butyl)ammonium perchlorate as supporting electrolyte, oxidation of [M^II(bpy)₃](ClO₄)₂ leads to the precipitation of a solid, electrochemically inactive phase of [M^III(bpy)₃](ClO₄)₃ (M = Co or Fe) on the electrode. Electrodes modified by this solid phase are shown to display catalytic waves that result from chemical reduction of the film by soluble species: [M(bpy)₃]⁺ when no other electroactive species is present or [C₆₀]^- when C₆₀ is also present in the solution. The redox behavior of C₆₀ on an electrode covered by a [Co^III(bpy)₃](ClO₄)₃ layer was extensively investigated. The catalytic current associated with the reduction of C₆₀ at a [Co^III(bpy)₃](ClO₄)₃ modified electrode can be used for the quantitative determination of fullerene concentration in solution. The reduction current associated with square wave voltammetric experiments increased linearly with the concentration of C₆₀ in the range of 0.25-20 μM. The detection limit is 0.1 μM. This method of fullerene quantitative determination exhibits good reproducibility, simplicity, and is relatively fast. Electrochemical oxidation of [Ru^II(bpy)₃](ClO₄)₂ does not produce an analogous redox inactive layer of [Ru^III(bpy)₃](ClO₄)₃.