COMPLEXES OF CU(II) WITH ELECTROACTIVE CHELATING LIGANDS ADSORBED ON GRAPHITE-ELECTRODES - SURFACE COORDINATION CHEMISTRY AND ELECTROCATALYSIS

Three electroactive chelating ligands, idyl)-5,6-di-phenyl-p,p'disulfo nate-1,2,4-triazine and 2,3-bis(2-pyridyl)pyrazine, were irreversibly adsorbed on pyrolytic graphite electrodes where their voltammetric res ponses were used to measure the quantities adsorbed. The adsorbed liga nds reacted with Cu2+ cations in solution to produce complexes adsorbe d on the electrode surface. The stoichiometric compositions of the ads orbed complexes were determined by means of coulometric assays of the quantities of ligand and Cu2+ present on the surface. The complex of C u2+ with 2,3-bis(2-pyridyl)pyrazine involved only one ligand per Cu2center and was catalytically active towards the reduction of O2 and H2 O2. The complexes formed with the triazine ligands contained two ligan ds per Cu2+ center and were not catalytically active. The pH dependenc ies of the formal potentials of the adsorbed complexes and of the half -wave potentials for the reduction of the substrates provided some ins ight into the mechanisms of the catalysed reductions.