The extent and dynamics of the adsorption on gold and pyrolytic graphite electrodes of four complexes of Os(II) were compared with the previously reported adsorption of similar complexes on Pt (Acevedo, D.; Abruna, 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 pyridine. 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 adsorbing complex. The adsorption appears to be driven by hydrophobic interactions of the organic ligands with the electrode surface and with each other as well as specific surface-ligand bond formation when a pendant 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 were not consistent with Langmuirian adsorption. Stabilizing intermolecular electronic interactions among the adsorbed molecules are suggested as a possible explanation for the observed behavior.