3-DIMENSIONAL MONOLAYERS - VOLTAMMETRY OF ALKANETHIOLATE-STABILIZED GOLD CLUSTER MOLECULES

Voltammetry of nonspecifically adsorbed and of freely diffusing monola yer protected clusters (MPCs) is presented. The MPC monolayers are mix tures of n-octanethiolates and omega-functionalized ferrocenyloctaneth iolates. MPC adsorption coverages range from a few percent to roughly a full monolayer of cluster molecules. Rotated disk electrode voltamme try of the ferrocenated MPCs has two principal features: the ferrocene oxidation wave and sloping current baselines at prewave and postwave potentials. Each MPC molecule can have multiple ferrocene units; chara cteristics of the ferrocene wave indicate that the polyelectron-transf er oxidations occur as a rapid sequence of single electron transfers. Comparisons of different modes of polyelectron transfer suggest that t he present one involves rotational diffusion. Deviation from ideal Ner nstian one-electron-transfer behavior is modeled as a Gaussian distrib ution of E-0' values. The sloping current baselines are attributed to double layer charging of the cluster cores that is controlled by hydro dynamic mass transport. Further aspects of previously described relati ons governing the core-charging property are compared to and found to be consistent with experimental behavior. Finally, preliminary experim ents for determining MPC diffusion coefficients by the Taylor dispersi on method are described.