1,1',2,2'-Tetra-methyl-3,3'-(p-phenyl-enedimethyl-ene)diimidazol-1-ium bis-(hexa-fluoridophosphate)

The title imidazolium-based ionic-liquid salt, C(18)H(24)N(4) (2+)·2PF(6) (-), has the cation lying about a center of inversion. The five-membered imidazole ring is disordered over two positions (the methyl substituents are ordered). This imidazole ring is approximately perpendicular to the six-membered phenyl-ene ring [dihedral angle = 81.3 (8)° for one disorder component and 83.8 (8)° for the other; the two components are off-set by 2.7 (8)°]. The crystal is a non-merohedral twin with a twin component of 23%.