The Cr(II) reduction of [Co(bpy)3]3+ proceeds by a series of steps which are accounted for by a complex and highly unusual mechanism. The chromium(III) product of the reaction is a dimer formulated as [Cr2(bpy)(OH)2(OH2)6]4+. The cobalt products include [Co(OH2)6]2+ and [Co(bpy)(OH2)4]3+. Intact free 2,2′-bipyridine and a reduced bipyridine species are also recovered. Four consecutive reactions are observed on the stopped-flow traces. The first one is independent of the [Cr(II)] concentration indicating that reduction has already occurred. The rate constant for this reaction is 46.3 ± 0.2 s-1. The second reaction is auto-catalyzed and has a rate constant of approximately (1.38 ± 0.2) × 102 s-1 assuming first order behavior. The thrid reaction is dependent on [Cr(II)] and has a rate constant kobs = k′3 + k″3[H+] where k′3 = 53 ± 3 M-1 s-1 and k″3 = (4.6 ± 0.2) × 102 M-2 s-1. The fourth reaction is independent of [Cr(II)] and has a rate constant kobs = k′4 + k″4[H+] where k′4 = 0.39 ± 0.02 s-1 and k″4 = 2.16 ± 0.06 M-1 s-1. A mechanism consistent with these observations is proposed.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry