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. Adsorption of the subject compounds occurred spontaneously and irreversibly at specific orientations which depended on their characteristic molecular structures and concentrations, C°. These orientations 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-diphenols or quinones, adsorption at C°: ≦ 0.1 mM produced flat-oriented (π-bonded) quinone intermediates; adsorption at C° ≧ 1 mM resulted in edge-oriented (di-σ-bonded) diphenolic species. When the Pt surface was purposely pretreated with π-bonded intermediates, severe reorientation retardation was observed, indicating that adsorption from concentrated solutions does not involve coordination in the flat orientation as an intermediate step. Substituents on or heteroatoms in the aromatic/quinonoid ring altered its surface coordination properties to varying degrees; analysis of the adsorption/orientation data enabled the formulation of a strength-of-chemisorption series for the various organic functional groups investigated. The effect of temperature on surface properties has been described in terms of perturbations to the preferred modes of attachment. Fluxional motion of chemisorbed 3,6-dihydroxypyridazine was indicated near 65 °C, similar to that of pyridazine itself in Pt coordination compounds.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry