ADSORPTION-DESORPTION PROCESSES OF REDOX-ACTIVE OSMIUM THIOL MONOLAYERS

The adsorption and desorption processes of a new series of redox-activ e transition metal complexes of the type [Os(bpy)(2)Cl(Py-(CH2)(n)-SH) ](PF6), with n = 4, 6, or 9, capable of forming adsorbed monolayers on gold and platinum electrodes have been studied using cyclic voltammet ry. The adsorption behavior of these osmium thiol complexes appears to be consistent with the Freundlich model. Although more than one equiv alent layer of the osmium complex was deposited, the multilayer was fo und to be porous. Variations in the pH of the deposition solutions fro m pH 1 to pH 5, as well as variations in the ionic strength of the sup porting electrolyte, had no effect on the amount of complex deposited. However, variations in the ionic strength of the supporting electroly te gave rise to changes in the formal potential of the osmium redox co uple which were ascribed to charge screening and Donnan effects. The d esorption reaction was described by a simple exponential expression. F rom the temperature dependence of the desorption rate and the Arrheniu s relationship, the activation energies for the desorption processes w ere determined. The activation energies were found to be dependent on both the length of the alkyl chain and the solvent used during desorpt ion. In addition, it was determined that after an 'annealing' time of 24 to 48 h there was a reorganization of the deposited multilayer to a lower energy form with a corresponding 20% increase in the activation energy for desorption, indicative of the multilayer reorganizing into a lower energy, more stable configuration.