Synthesis and characterisation of ionic liquids based on 1-butyl-3-methylimidazolium chloride and MCl4, M = Hf and Zr

Abstract

Dialkylimidazolium chlorometallate molten salts resulting from the combination of zirconium or hafnium tetrachloride and 1-butyl-3-methylimidazolium chloride, [C₁C₄Im][Cl], have been prepared with a molar fraction of MCl₄, R = n_MCl4/n_MCl4 + n_[C1C4IM][Cl] equal to 0, 0.1, 0.2, 0.33, 0.5, 0.67. The structure and composition were studied by Differential Scanning Calorimetry (DSC), ³⁵Cl (263 to 333 K), ¹H and ¹³C solid state and solution NMR spectroscopy, and electrospray ionisation (ESI) mass spectrometry. The primary anions of the MCl₄-based ILs were [MCl₅], [MCl₆] and [M₂Cl₉], whose relative abundances varied with R. For R = 0.33, pure solid [C₁C₄Im]₂[MCl₆], for both M = Zr and Hf are formed (m.p. = 366 and 385 K, respectively). For R = 0.67 pure ionic liquids [C₁C₄Im][M₂Cl₉] for both M = Zr and Hf are formed (T_g = 224 and 220 K, respectively). The thermal dissociation has been attempted of [C₁C₄Im]₂[HfCl₆], and [C₁C₄Im]₂[ZrCl₆] monitored by ³⁵Cl and ⁹¹Zr solid NMR (high temperature up to 551 K).