Synthesis, crystal structures and electrical conductivities of the ionic liquid compounds butyldimethylimidazolium tetrafluoroborate, hexafluorophosphate and hexafluoroantimonate

Abstract

The crystal structures of three very low-melting ionic liquid (IL) salts containing the 1-butyl-2,3-dimethylimidazolium cation and the fluoro anions BF4-, PF6- and SbF6- are reported. These are considered model compounds for ambient temperature ionic liquids, which are currently being explored as solvents for various types of synthetic reactions. All three compounds adopt significantly different structures in the solid state, highlighting the influence of counterion size in a series comprising a common cation. The crystal structures are discussed with respect to the possible existence of polar and non-polar domains, which are considered to be involved with the solvation of polar and non-polar substrates. The melting points of all three compounds are within the range 40-45 °C. A comparative measurement of conductivities of the molten salts in the vicinity of 20-50 °C has been made, including the new IL 1-allyl-2,3-dimethylimidazolium tetrafluoroborate and the widely applied 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF4). © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.