Solubility Behaviour of TiCl4, ZrCl4, and HfCl4 in Chloroaluminate Ionic Liquids

The solubility of NbCl₅, TaCl₅, TiCl₄, ZrCl₄, and HfCl₄ in neutral [BMIM][AlCl₄] (BMIM = 1‐butyl‐3‐methylimidazolium) was determined. While TiCl₄ was immiscible with the neutral ionic liquid, 0.80 molar equivalents of ZrCl₄ and stoichiometric amounts of HfCl₄ dissolved in the melt at ambient temperature. The crystal structures and the unit cell parameters of [BMIM]₂[Ti₂Cl₁₀], [BMIM]₂[Zr₂Cl₁₀], and [PhNMe₃][Hf₂Cl₉] were determined. [BMIM]₂[Ti₂Cl₁₀], and [BMIM]₂[Zr₂Cl₁₀] were crystallised from basic chloroaluminate melts. With a trimethylanilinium cation, [PhNMe₃][Hf₂Cl₉] crystallised from an equimolar composition of PhNMe₃Cl, AlCl₃, and HfCl₄. Obviously, HfCl₄ abstracted a chloride ligand from [AlCl₄]^– to give highly Lewis acidic [Al₂Cl₇]^– anions.