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Polarographic Studies of Metallic Complexes. III. Pentammine Series of Cobalt (III) Complexes

1959; Oxford University Press; Volume: 32; Issue: 1 Linguagem: Inglês

10.1246/bcsj.32.23

1348-0634

Nobufumi Maki, Yoichi Shimura, Ryutaro Tsuchida,

Analytical Chemistry and Sensors

Abstract 1. Most of the cobalt(III) complex ions of pentammine series, [Co(NH3)5X](3−n)+, are reduced irreversibly in two steps at the dropping mercury electrode. The first diffusion current corresponds to the reduction, cobalt(III) → cobalt(II) and the second to the reduction, cobalt(II) → cobalt(0). The diffusion current and concentration were linearly related. 2. The polarographic stability of cobalt (III) complexes of the pentammine series increases in the following order of the ligands; I−, Br−, Cl−, CrO42−, NCS−<NO3− <N3−<SO42−<NO2−<C2O42− <CH3COO−<NH3<OH2<OH− <CO32−, HCO3− (Supporting electrolyte; 0.5 F potassium sulfate). The reverse of the order was found between carbonate and water molecule when 0.1 F potassium chloride was used as a supporting electrolyte. This order did not agree with that of the spectrochemical series of the pentamminecobalt(III) complexes. 3. In dilute perchloric acid the welldefined wave was obtained for aquopentamminecobalt (III) ion, [Co(NH3)5OH2]3+, while the ion gave a modified wave in the first reduction step in neutral supporting electrolyte, potassium chloride or potassium sulfate.