Cyclic Voltammetry and Chronocoulometry with trans-Rh(en)[sub 2]Cl[sub 2]+] at Mercury Electrodes

Abstract

Cyclic voltammetric, coulometric, and chronocoulometric data associated with the reduction of Rh(en)2Cl~ + at mercury electrodes are reported that confirm previous results indicating the occurrence of a two-electron reduction to produce the hydrido complex, Rh (en)2H (OH2)2+ which engages in a pH dependent equilibrium involving Rh(en)2+: Rh(en)2H(OH2) ~+ + OH-Rh(en)~ + + 2H20. The resulting presence of Rh(en)2 + at the electrode surface has a number of interesting consequences which are described. Among these are the electrochemical production of metal-metal bonded rhodiummercury adducts, apparent strong adsorption of Rh(en)~ + on the electrode surface, and anomalous cyclic voltammograms with inverted peaks.

Electrochemistry and Adsorption of Bis 2,2′‐Bipyridinecobalt(I) and Bis 6,6′‐Dimethyl‐2,2′‐Bipyridinecobalt(I) in Acetonitrile

“…Increasing the d electron density on the cobalt by reduction to cobalt(0) would be expected to favor the formation of a metal-metal bond with mercury. Similar surface coordination chemistry leading to adsorption on mercury was encountered in previous studies with low-valent complexes of cobalt (13) and rhodium (14).…”

Direct Reduction of Alkyl Monohalides at Silver in Dimethylformamide: Effects of Position and Identity of the Halogen

“…5); such peaks have been observed before in our laboratory [46] and an explanation for these types of peaks is found in research by Gulen, Konrad, and Anson. [47] Furthermore, exposure time of the silver electrode to the electrolyte solution containing 2 mM 1a at the initial potential of the cyclic voltammogram does not alter the peak currents for exposure times between 5 and 600 s.…”

Electrochemical reduction of at Hg/phosphate electrolyte interface

“…The strong tendency of RhðbpyÞ 3þ 3 to form adsorbed layers made it seem likely that this complex would be involved in the formation of rhodium-mercury bonds as in the case of Rh-ethylenediamine complexes [30,31]. Indeed, the formation of chemical bond between the complex and mercury is the most plausible explanation for the observed electrochemical behavior.…”

“…The stripping-like character of the I a peak indicates the accumulation of the reduction products at the surface of the electrode, stressing the important role of mercury in the electroreduction. To make the interpretation of the voltammograms even more difficult, Rh-complexes can easily form covalent bond with mercury, resulting in mixed Hg-Rh complexes [29][30][31].…”

“…The plausible explanation for this interesting behavior is that the RhðbpyÞ 3þ 3 complex is strongly adsorbed at mercury electrode and undergoes slow chemical transformation at its surface. Chemical transformation is potential dependent, and it is very likely that some kind of rhodium adduct of mercury, which is known to occur in this kind of systems [29][30][31] is formed. At low scan rates chemical reaction has ample time to take place, resulting in the product which is reduced at the potentials of III c current peak.…”