Vanadium Complexes in a Lewis Basic Room-Temperature 1-Ethyl-3-methyl-1H-imidazolium Chloride/Aluminum Chloride Molten Salt

Complexes of VCl3 and VCl4 have been formed in a Lewis basic room-temperature molten salt consisting of 1-ethyl-3-methyl-1H-imidazolium chloride and aluminum chloride. Electrochemical and spectroscopic studies show that 3 equiv of chloride can be added to VCl3 to form higher order chloride complexes. Each vanadium(III) complex can be reversibly oxidized to a corresponding vanadium(IV) complex. The potentials for the couples VCl4 - ↔ VCl4 + e-, VCl5 2- ↔ VCl5 - + e-, and VCl6 3- ↔ VCl6 2- + e- occur at 1.33, 1.23, and 1.00 V, respectively, measured versus a reference electrode consisting of an aluminum wire in a 0.6 mole fraction AlCl3 melt. Although higher order chloride complexes of other transition metals have been reported in these melts, this is the first metal for which the stepwise addition of chloride accompanied by reversible electrochemistry for each species has been demonstrated. This also shows that molten salts are useful for stabilizing complexes which may be hydrolyzed by the residual water sometimes present in organic solvents.