Surface Coordination Chemistry of Platinum Studies by Thin-Layer Electrodes. Adsorption, Orientation, and Mode of Binding of Aromatic and Quinonoid Compounds

摘要

Extensive studies on the interaction of 54 aromatic and quinonoid compounds with smooth Pt thin-layer electrodes have yielded data that serve to establish the surface coordination chemistry of polycrystalline Pt with these compounds in aqueous solutions. Absorption of the subject compounds occurred spontaneously and irreversibly at specific orientations which depended on their characteristic molecularr structures and concentrations, C. These orientations which have been represented in terms of modes of coordination derived from model compounds; supportive electrochemical and infrared spectroscopic data are presented. For simple o- and p-diphennols or quinones, absorption at C < or = 0.1 mM produced flat-oriented (pi-bonded) quinone intermediates; adsorption at C < or = mM resulted in edge-oriented (di-pi-bonded) diphenolic species. When the Pt surface was purposely pretreated with pi-bonded intermediates, severe reorientation retardation was observed, indicating that absorption from concentrated solutions does not involve coordination in the flat orientation as an intermediate step. Substituents on or heteroatoms in the aromatic/quiinonoid ring altered its surface coordination properties to varying degrees; analysis of the absorption/orientation data enabled the formulation of a strength-of-chemisorption series for the various organic functional groups investigated. The effect of temperature on surface propertiees has been described in terms of perturbations to the preferred modes of attachment.