Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Polarographic Behavior of Tris(2,2′-bipyridine)cobalt(II) and Tris(2,2′-bipyridine)cobalt(III) in Acetonitrile Solutions
Nobuyuki TanakaYuichi Sato
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1968 Volume 41 Issue 9 Pages 2059-2064


The electrode processes of tris(2,2′-bipyridine)cobalt(II) and tris(2,2′-bipyridine)cobalt(III) complexes at the dropping mercury electrode in acetonitrile solutions have been investigated by the measurement of direct current, alternating current and Kalousek polarograms. The cobalt(II) complex gave a one-step oxidation and a four-step reduction wave and the cobalt (III) complex, a five-step reduction wave, when tetraethylammonium perchlorate was used as supporting electrolyte. The solution containing the cobalt(II) and the cobalt(III) complexes gave a reversible composite wave. The limiting currents of the first two steps named from positive to negative potentials of the reduction wave of the cobalt(II) complex were diffusion-controlled, the first step being of a one-electron reduction process and the second step, of a two-electron reduction process. From the effect of free 2,2′-bipyridine and water on the reduction wave of the cobalt(II) complex and from the Kalousek polarograms, the electrode processes of the first two steps taking place in the presence of a large concentration of free 2,2′-bipyridine were estimated as,
[Co(bipy)_3]^2+\oversete\underset-e\ ightleftharpoons[Co(bipy)_3]^+\overset2e\underset-2e\ ightleftharpoons[Co(bipy)_3]^-
The effect of a small concentration of acrylonitrile on the reduction wave of the cobalt(II) complex was studied.

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