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.
Reduction of Hexamminechromium(III) Ions at the Dropping Mercury Electrode
The reduction of hexamminechromium(III) ion at the dropping mercury electrode has been studied in neutral and acid aqueous solutions. Hexamminechromium(III) ion gives no well-defined d. c. polarographic wave in an unbuffered neutral solution, whereas in an acid solution it gives a well-defined two-step wave, the first wave corresponding to the reduction of chromium(III) to chromium(II) and the second, to that of chromium(II) to chromium-(0).The first wave of the d. c. polarogram obtained in an acid solution is diffusion-controlled and gives a slope of the log-plot close to that expected for a reversible wave. The a. c. and the Kalousek polarogram, however, are of the irreversible type. No chemical reaction involving hydrogen ions, ammonium ions or ammonia takes place preceding the electron transfer. Considering these results, the following mechanism is temporarily suggested for the reduction of hexamminechromium(III) ions at the dropping mercury electrode:[Cr(NH3)6]3++e\ightleftarrows[Cr(NH3)6]2+[Cr(NH3)6...
Über eine Verbindung des 1‐wertigen Chroms: [Dipy3Cr]ClO4
Als erste definierte Cr(I)-Verbindung wurde das Tri-α,α'-Dipyridyl-Chrom(I)-perchlorat dargestellt und kurz charakterisiert.