THERMODYNAMICS OF ADSORPTION OF REDOX-ACTIVE SELF-ASSEMBLING MONOLAYERS OF TRANSITION-METAL COMPLEXES

The redox-active self-assembling system [Os(bpy)2LCl]+ (bpy = 2,2'-bip yridine; L = 4,4'-bipyridine e(dipyH2),trans-1,2-bis(4-pyridyl)ethylen e(py=py), or 1,3-bis(4-pyridyl)-propane (dipy)) has been studied, usin g voltammetric methods, to investigate the dependence of the depositio n potential, pH, and ionic strength on the thermodynamics of the self- assembling process. Repulsive electrostatic interactions are believed to give rise to (i) variations in the adsorption isotherms, (ii) shift s in E-degrees' as a function of surface coverage, and (iii) differenc es in surface coverage between the reduced (Os(II)) and oxidized (Os(I II)) forms of the complexes. A lowering of the pH of the deposition so lution decreased the amount of adsorbate available for deposition so t hat lower unitary values were obtained. Finally, the ionic strength of the supporting electrolyte affected neither the adsorption equilibriu m nor the thermodynamics of adsorption but did give rise to variation in the formal potential, probably due to charge screening effects.