Spectroscopic and Electrochemical Studies of Tungsten(VI) and Tungsten(V) Chloride and Oxychloride Complexes in a Sodium Chloride Saturated Sodium Chloroaluminate Melt

Raman and UV-visible absorption spectroscopies indicate that the addition of WCl[sub 6] or KWCl[sub 6] to a sodium chloride saturated sodium chloroaluminate melt at 175 C produces the tungsten (V) hexachloride anion [WCl[sub 6]][sup [minus]] can be oxidized to WCl[sub 6] via a reversible one-electron charge-transfer process with a voltammetric half-wave potential of 2.077 V referenced to aluminum in a pure sodium chloride saturated sodium chloroaluminate melt. With fast scan rate voltammetry, [WCl[sub 6]][sup [minus]] can be reduced to [WCl[sub 6]][sup 2[minus]] and [WCl[sub 6]][sup 3[minus]] via two consecutive one-electron reduction processes with half-wave potentials of 1.578 and 0.818 V, respectively. Both [WCl[sub 6]][sup 2[minus]] and [WCl[sub 6]][sup 3[minus]] form precipitates in this melt at this temperature. Using slow scan rate voltammetry, the reduction processes are complicated by coupled chemical reactions. Tungsten (VI) oxychloride, WOCl[sub 4], is stable in this melt, and can be reduced to tungsten (V) oxychloride via a reversible one-electron reduction process with a half-wave potential of 1.746 V. Absorption spectroscopy shows that the tungsten(V) chloride is [WOCl[sub 5]][sup 2[minus]]. Fast scan rate voltammetry indicates that tungsten (V) oxychloride exhibits a two-electron reduction process to produce a W(III) species. At slow scan rates, the reduction appears tomore » be complicated by coupled chemical reactions. Definitive characterization of the reduction mechanisms is prevented by film formation on the electrode surface during these reductions.« less