Electrode reactions of tris(2,2′-bipyridine)-iron(II) and tris(2,2′-bipyridine)iron(III) complexes in acetonitrile solution

Abstract

The electrode processes of tris(2,2′-bipyridine)iron(II) and tris(2,2′-bipyridine)iron(III) complexes at the rotated platinum electrode and the dropping mercury electrode (dme) in acetonitrile solutions have been investigated by the measurement of current/potential curves, dc and ac polarograms and Kalousek polarograms. The system of the iron(II) and the iron(III) complex was reversible at the rotated platinum electrode. The iron(II) complex gave a five-step reduction wave at the dme when tetraethylammonium perchlorate was used as supporting electrolyte. The limiting currents of the first three steps named from positive to negative potentials were all diffusion-controlled and of a one-electron reduction processes. From the effect of free 2,2′-bipyridine and water on the reduction wave of the iron(II) complex and from the shape of Kalousek polarograms, the electrode processes for the first three steps are concluded to be the reductions from [Fe(bipy)3]2+, [Fe(bipy)3]+ and [Fe(bipy) 3], respectively. It has been proposed that at the third step univalent tris(2,2′-bipyridine)-ferrate anions, [Fe(bipy)3]−, are formed at the electrode surface in acetonitrile.