ELECTROCHEMISTRY OF TANTALUM(V) CHLORIDE IN THE BASIC ALUMINUM CHLORIDE-1-METHYL-3-ETHYLIMIDAZOLIUM CHLORIDE ROOM-TEMPERATURE MOLTEN-SALT

Electronic absorption spectroscopy indicated that tantalum(V) is complexed as [TaCl6]− in the basic AlCl3-1-methyl-3-ethylimidazolium chloride molten salt. This anionic species can be reduced to [TaCl6]2− in a one-electron, reversible electrode reaction with a voltammetric half-wave potential of −0.49V in the 44.4/55.6 m/o melt vs. the Al3+/Al couple in the 66.7/33.3 m/o melt at 40°C. Voltammograms of [TaCl6]− solutions also exhibit a second reduction process with a voltammetric peak potential of about −1.70V us. this same reference electrode. This second electrode reaction is complicated by coupled homogeneous chemistry at slow scan rates but appears to simplify to a one-electron reduction process at fast scan rates. The average Stokes-Einstein products for [TaCl6]− and [TaCl6]2− are 3.5 × 10−10 and 1.9 × 10−10 g cm s−2 K−1, respectively. The former complex, but not the latter, appears to react slowly with oxide in the melt to form an oxide-containing complex. The conditional equilibrium constant for the reaction between oxide and [TaCl6]− is approximately 1.4 ± 0.3 × 103. The tantalum(V) oxide-containing species can be converted back to its chloride complex with COCl2. © 1990, The Electrochemical Society, Inc. All rights reserved.