An Investigation of the Symmetric and Asymmetric Cleavage Products in the System Aluminum Trihalide/1-Butylimidazole.

Mixtures of AlX3 (X=Cl, Br) with 1-butylimidazole (BuIm) in various ratios were investigated. The mixtures were characterized by multinuclear (1 H, 27 Al, 13 C, and 15 N) NMR, IR, and Raman spectroscopy and in part by single-crystal X-ray diffraction. Depending on the molar fraction x(AlBr3 ) of the AlBr3 -based mixtures, the cationic aluminum complexes [Al(BuIm)6 ]3+ and [AlBr2 (BuIm)4 ]+ , the neutral adduct [AlBr3 (BuIm)], as well as the anions Br- , [AlBr4 ]- , and [Al2 Br7 ]- could be identified as the products of the symmetric and asymmetric cleavage of dimeric Al2 Br6 . Furthermore, there are hints at the formation of [AlBr2 (BuIm)2 ]+ or related cations. Comparison of the AlBr3 /BuIm system with AlCl3 -based mixtures revealed the influence of the halide: In contrast to AlBr3 , the trication [Al(BuIm)6 ]3+ could not be detected as main product in a 1:6 mixture of AlCl3 and BuIm. Additionally, [AlCl3 (BuIm)] crystallizes from a mixture with x(AlCl3 )=0.60 at room temperature, whereas the corresponding AlBr3 -based mixture remains liquid even at +6 °C. Three AlBr3 -based mixtures are liquid at room temperature, whereas all other mixtures are solids with melting points between 46 and 184 °C. The three liquid mixtures exhibit medium to high viscosities (117 to >1440 mPa s), low conductivities (0.03-0.20 mS cm-1 ), but high densities (1.80-2.21 g cm-3 ). Aluminum could be successfully deposited from one of the neat Lewis acidic mixtures of the AlBr3 -based system.

Synthesis and Characterization of Bromoaluminate Ionic Liquids.

Twelve bromoaluminate based ionic liquids (ILs) were synthesized and characterized by IR, Raman, and NMR spectroscopy, as well as single crystal X-ray diffraction in part. Their principal physicochemical properties including melting points, conductivities, viscosities, and densities were determined and compared with related ILs. The influence of the cation and anion on the physicochemical properties are discussed. The [AlBr4 ]- based salts are-with one exception-solid at room temperature, while the compounds based on the anion [Al2 Br7 ]- are liquid at room temperature. The liquid salts show low viscosities (49-139 mPa s), medium to high conductivities (0.76-3.53 mS cm-1 ) and high densities (1.82-2.04 g cm-3 ) at 28 °C. Furthermore, we showed aluminum electrodeposition from Lewis acidic ILs based on AlBr3 and 1-hexyl-3-methylimidazolium bromide and investigated the stability range of various formulations.