Electrochemical studies of chromium(III) and chromium(II) chloride complexes in basic aluminum chloride-1-methyl-3-ethylimidazolium chloride room temperature molten salts

Chromium(III) chloride is complexed as [CrCl6](3-) in the basic aluminum chloride-1-methyl-ethylimidazolium chloride melt, and it can be reduced to a Cr(II) species at a glassy carbon electrode. Absorption spectroscopy and titration experiments suggest that the Cr(II) is complexed as [CrCl4](2-). The Cr(III)/Cr(II) electrode reaction exhibits slow charge-transfer kinetics with a standard heterogenous rate constant of 3.27 x 10(-6) cm s(-1) and a cathodic transfer coefficient of ca. 0.38 in the 44.4/55.6 mole percent (m/o) melt at 27 degrees C. The formal electrode potential of the Cr(III)/Cr(II) chloride redox couple is -0.649 V in the 44.4/55.6 m/o melt. The Stokes-Einstein products of [CrCl6](3-) and [CrCl4](2-) complexes are 1.2 x 10(-10) and 1.7 x 10(-10) g cm s(-2) K-1, respectively.