Structural Studies of Crystalline 1-Alkyl-3-Methylimidazolium Chloride Salts

The structures of three long alkyl chain imidazolium chloride salts have been determined by X-ray diffraction; one of the salts was isolated as two polymorphs. These compounds consist of regions containing interdigitated linear alkyl chains alternating with regions containing imidazolium headgroups, chloride ions, and solvent. The arrangement of the cation headgroup and the alkyl chain is strongly dependent on the thermal history of the salt and whether the C(2) position on the imidazolium ring is methylated or protiated. Structures are found where the headgroups within the same crystal are in different environments leading to a double bilayer structure which collapses on heating.