Polarographic Behaviour of the Hexa-ammine-chromium(III) Ion: Role of Hydrogen Ions
HEXA-AMMINECHROMIUM(III) ion in acetate buffer solutions is reduced at the dropping mercury electrode, and gives two polarographic waves. The first wave, which is well defined, is considered to be a one-electron reduction of Cr(III) to Cr(II)1. Its half-wave potential at 25° C was found to be −0.970 V versus saturated calomel electrode in 0.1 M acetate buffer solution which contained 0.9 M potassium chloride and 0.005 per cent gelatin (Fig. 1, curve a). The limiting current of this wave was diffusion-controlled and proportional to the concentration of the complex ion up to 5 mM. Both the half-wave potential and the diffusion current remained constant when the pH was varied from 4.5 to 5.45. No change was observed when potassium chloride was replaced by ammonium chloride at the constant ionic strength. The plot of log ī/(īd − ī) versus E, where ī means the average current, īd the average diffusion current, and E, the potential of the dropping mercury electrode, gave a straight line with a reciprocal slope of 64 mV, whereas the examinations with Kalousek's circuit and alternating current polarograph showed that this wave has nearly irreversible character.
Polarographic Behaviour of Chromium-Dipyridyl Complexes
IT has been shown previously that dipyridyl (dipy) complexes of cobalt and nickel are reduced at the dropping-mercury electrode with the formation of uni- and zero-valent complexes, respectively1,2. Further work led to the conclusion that iron(II)–dipyridyl complex is not reduced at the dropping mercury electrode and that the complex Mn(dipy)32+ is reduced with the formation of manganase(I) complex (unpublished results).
Polarographic Studies of Metallic Complexes. I. Oxalato-ammine, Glycinato-ammine and Ethylenediamine-ammine Series of Cobalt (III) Complexes
The ions [Co oxn(NH3)6−n](2l−3)−, [Co glyn(NH3)6−n](3−l)+,[Co enn(NH3)6−n]3+, [Co en2 gly]2+ and [Co en2 ox] + were all reduced irreversibly in two steps at the dropping mercury electrode.The first diffusion current corresponds to the reduction, CoIII→CoII and the second to the reduction, CoII→Co0. The diffusion current and the concentration were linearly related.The half wave potential of the first wave of the cobalt (III) complexes shifts to negative direction in the following order of the ligands: ox2−, gly−, NH3, en.