Maurice L’Her

Electrodes modified by conducting polymers bearing redox sites: Ni- and Co-cyclam complexes on polypyrrole

Abstract Cyclam has been N-functionalized and linked to the nitrogen of pyrrole through an alkyl spacer. After complexation of the ligand by nickel(II) or cobalt(II), the complexes have been electropolymerized on the surface of electrodes, by cyclic voltammetry or at constant potential. The Ni(III)/Ni(II) redox system is very distinctly visible on the voltammogram of the poly[Ni(II)-cyclam- N -(CH 2 ) 5 -pyrrole] film, even after over-oxidation of the polypyrrole backbone; from this observation it is obvious that the electron transfer between nickel sites occurs through hopping. The electropolymerization of Co(III)-cyclam- N -(CH 2 ) 5 -pyrrole is more difficult and the films are thin and brittle; those obtained from the electropolymerization of the Co(II) complex are of a better quality. The Co modified glassy carbon electrodes are active for the electrocatalytic reduction of dioxygen in acidic media. A gold electrode modified by poly[Co(III)-cyclam- N -(CH 2 ) 5 -pyrrole] catalyses the nitrate ion reduction at −1.0 V versus saturated calomel electrode (SCE) in a strongly basic medium, after amalgamation.

Substituent effect in unsymmetrical lutetium bisphthalocyanines: a DFT analysis

DFT calculations have been carried out on a series of unsymmetrical bisphthalocyanine lutetium complexes in which one of the ligands is substituted by 8 or 16 chlorine atoms. It is shown that their unpaired electron is predominantly localized on the non-substituted ligand. An orbital explanation is provided to rationalize this effect. A good agreement is found between the computed and experimental ionization potentials and electroaffinities and the redox potentials of a closely related series, as well as between their TDDFT-computed and experimental UV-visible transitions which are analysed.

Electrocatalytic reduction of dioxygen to water by tren-capped porphyrins, functional models of cytochrome c oxidase†

Two different tren-capped porphyrins—in which the two metals, iron and copper, are more or less off-centered—are shown to be efficient catalysts for the reduction of O2 to H2O; surprisingly, their iron-only complexes are shown to be even more effective 4e– catalysts when adsorbed on a graphite electrode.