Double-Layer Effects on Simple Electrode Reactions. III. The Reduction of Eu(3+) and Cr(3+) in the Presence of Thiocyanate Anions. Evidence for Ligand Bridging.

摘要

The rates of reduction of Eu(3+) and Cr(3+) have been measured in mixed perchlorate + thiocyanate electrolytes at constant ionic strength, using low concentrations of thiocyanate to minimize its association with the cationic reactants. The effect of adsorbed thiocyanate anions on the reduction kinetics of Cr(3+) resembled those produced by iodide and bromide on both Cr(3+) and Eu(3+). However, thiocyanate exhibited an unusual catalytic effect on the reduction of Eu(3+) which was identified as arising from a reaction pathway involving thiocyanate-bridging between the mercury surface and the Eu(3+). The diagnostic criteria used to support the proposed mechanism included analysis of the rate-potential behavior and of the effects of competitively adsorbed iodide ions upon the reduction rates. (Author)