Electrochemistry of bipyridyl derivatives of cobalt in solutions of anionic and cationic micelles

Abstract

Electroreductions of tris(2,2′-bipyridyl) and 4,4′-dimethyl-2,2′-bipyridyl complexes of Co(II) in 0.1 M solutions of sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) were investigated. Electrochemical, UV and NMR results showed that all complexes studied were bound to micellar aggregates. Co(II) complexes were bound close to the Stern layer of SDS micelles, and to hydrophobic regions of CTAB micelles. Differences in the distribution of the complexes are explained in terms of coulombic and hydrophobic interactions of solutes with the micellar aggregates. Rates of electron transfer were slower in surfactant solutions than in acetonitrile (MeCN), following the order MeCN > CTAB > SDS. Dimethylbipyridyl and long chain bpyC16 complexes gave slower electron transfer than Co(bpy)2+3. Also, equilibria and/or kinetics of dissociation of Co(bpy)−3, Co(dmbpy)+3, and Co(dmbpy)−3 were altered in CTAB as compared to acetonitrile. Co(−I) complexes reduced water in SDS, but not in CTAB. Adsorption of some Co(I) and Co(−I) complexes at the glassy carbon electrode occurred in CTAB.