Electrochemistry of surface grafted copper(II) benzoate complexes

Glassy carbon electrodes were grafted with carboxyphenyl groups by reduction of 4-carboxyphenyldiazonium tetrafluoroborate and these modified electrodes were characterised by cyclic voltammetry and ac impedance measurements. Cu(II) was reacted with the carboxyphenyl groups in the film to give a surface voltammetric response for the immobilised Cu(II)/Cu(I) couple. The results indicated an ECEC mechanism, in which the chemical steps correspond to the change of coordination environment following the electron transfer steps. The relaxation half-life time for the Cu(I) species formed after electron transfer was estimated at (140 ± 11) s. The large value of the peak width of ∼200 mV was analysed by modelling the voltammograms and the large value of the full width at half maximum (FWHM) could be explained by dispersion in the formal potentials of Cu centres present in a variety of environments in the films studied. An ECEC mechanism (scheme of square) is proposed for the electron transfer reaction considering that the chemical step after reduction of the Cu(II) complex corresponds to conformational changes within the attached layer. Experimental data clearly show that the oxidation of the reduced film can take place from different Cu(I) complexes formed along the reduction to the fully relaxed Cu(I) species.