FACTORS RESPONSIBLE FOR THE UNUSUALLY STRONG ADSORPTION OF [OS(BPY)(2)(CL)L(1)](-BIS(4-PYRIDYL)ETHANE) AND RELATED COMPLEXES ON METAL AND GRAPHITE ELECTRODE SURFACES() (L(1)=1,2)

The extent and dynamics of the adsorption on gold and pyrolytic graphi te electrodes of four complexes of Os(II) were compared with the previ ously reported adsorption of similar complexes on Pt (Acevedo, D.; Abr una, H. D. J. Phys. Chem. 1991, 95, 9590). The complexes investigated were [Os(bpy)(2)(Cl)L](+) with bpy = 2,2'-bipyridine and L = 1,2-bis(4 -pyridyl)ethane, 4-phenylpyridine, 4-(1-n-butylpentyl)pyridine, and py ridine. Spontaneous, strong adsorption of all four complexes occurred on graphite electrodes and, except for the complex with L = pyridine, on gold electrodes. The presence of a pendant pyridine site on ligand L is not required for strong adsorption to occur. Replacement of the [ Os(bpy)(2)(Cl)](+) center by RU(NH3)(5)(2+) also led to a strongly ads orbing complex. The adsorption appears to be driven by hydrophobic int eractions of the organic ligands with the electrode surface and with e ach other as well as specific surface-ligand bond formation when a pen dant pyridine group is present. Although the concentration dependence of the quantities of the complexes adsorbed could be fit to a Langmuir isotherm, the dynamics of the adsorption and desorption reactions wer e not consistent with Langmuirian adsorption. Stabilizing intermolecul ar electronic interactions among the adsorbed molecules are suggested as a possible explanation for the observed behavior.