Imidazolium-based ionic liquid salts: 3,3'-dimethyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(tetrafluoroborate) and 3,3'-di-n-butyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(trifluoromethanesulfonate)

Crystallization of the ionic liquid 3,3'-dimethyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(tetrafluoroborate), C(16)H(20)N(4)(2+).2BF(4)(-), (I), from its solution in water has permitted the first single-crystal study of an imidazolium-based ionic liquid having a tetrafluoroborate ion as counter-ion. Despite the expectation that the anion would not participate in nonclassical hydrogen bonding, the ionic liquid features C-H...F hydrogen bonds. The dication lies about a center of inversion. The ionic liquid 3,3'-di-n-butyl-1,1'-(1,4-phenylenedimethylene)diimidazolium bis(trifluoromethanesulfonate), C(22)H(32)N(4)(2+).2CF(3)SO(3)(-), (II), features both C-H...F and C-H...O hydrogen bonds.