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Polarographic Studies of Metallic Complexes. II. Isothiocyanato-ammine and Related Complexes of Chromium (III)

1958; Oxford University Press; Volume: 31; Issue: 4 Linguagem: Inglês

10.1246/bcsj.31.413

1348-0634

Nobufumi Maki, Yoichi Shimura, Ryutaro Tsuchida,

Inorganic and Organometallic Chemistry

Abstract 1. In neutral and unbuffered solution of 0.1 f potassium chloride, 0.1 f potassium thiocyanate, or 1 f potassium thiocyanate, the complex ion, [Cr(NH3)n(NCS)6−n]n−3 and [Cr en3]3+ were all reduced irreversibly in two steps at the dropping mercury electrode. The first diffusion current corresponds to the reduction, chromium(III)→chromium(II), and the second to the reduction, chromium(II)→chromium(0). 2. In the solution of 0.1 f potassium chloride, the polarograms of [Cr en2X2]+ type complexes show three waves. Each of the first two waves, corresponding to a gain of one electron, represents the reduction of chromium(III) to chromium(II) and the last wave, corresponding to a gain of two electrons, represents the reduction to the metallic state. As regards the first two waves, the former wave represents the reduction of the original chromium(III) complexes to chromium(II) state and the latter represents the reduction of the aquated chromium(III) complexes to chromium(II) state. 3. In agreement with the results obtained for cobalt(III) complexes by Holtzclaw et al., the trans isomer of [Cr en2(NCS)2]+ has a little more negative half-wave potential than the corresponding cis-form. 4. The polarographic stabilities of chromium(III) complexes increase in the following order of the ligands: Cl^-<NCS^-<en<NH_3 5. The catalytic effects on the double wave of oxygen have been found for [Cr(NH3)2(NCS)4]−, [Cr(NCS)6]3−, or cis-[Cr en2(NCS)2]+. Such special polarographic behavior was not found in the other chromium(III) complexes.