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)
Jle. Campbell et Fc. Anson, 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), Langmuir, 12(16), 1996, pp. 4008-4014
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.