Three electroactive chelating ligands, 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine,3-(2-pyridyl)-5,6-di-phenyl-p,p′disulfonate-1,2,4-triazine and 2,3-bis(2-pyridyl)pyrazine, were irreversibly adsorbed on pyrolytic graphite electrodes where their voltammetric responses were used to measure the quantities adsorbed. The adsorbed ligands reacted with Cu 2+ cations in solution to produce complexes adsorbed on the electrode surface. The stoichiometric compositions of the adsorbed complexes were determined by means of coulometric assays of the quantities of ligand and Cu 2+ present on the surface. The complex of Cu 2+ with 2,3-bis(2-pyridyl)pyrazine involved only one ligand per Cu 2+ center and was catalytically active towards the reduction of O 2 and H 2O 2. The complexes formed with the triazine ligands contained two ligands per Cu 2+ center and were not catalytically active. The pH dependencies of the formal potentials of the adsorbed complexes and of the half-wave potentials for the reduction of the substrates provided some insight into the mechanisms of the catalysed reductions.