Solid-State Structures of Double-Long-Chain Imidazolium Ionic Liquids: Influence of Anion Shape on Cation Geometry and Crystal Packing

The syntheses and solid-state structures of a series of imidazolium (IM) salt-based, double C12 alkyl chain functionalized ionic liquids, namely, [C12C12IM][A], where the anion A is I−, I3−, I5−, N(CN)2−, C(CN)3−, B(CN)4−, or SbF6−, are reported. All compounds were fully characterized by CHN elemental analysis, 1H and 13C NMR spectroscopy, and X-ray diffraction studies on single crystals. The molecular structure of the IM [C12C12IM]+ cation, as found in the individual crystal packing arrangements, is discussed in relation to the different anions used for crystallization. Depending on the geometry of the counteranions used (linear, bent, planar, and spherical), different molecular structures of the IM cations (rod-, V-, and U-shaped) resulted. The crystal packing in the solid-state structure is examined on the basis of a Hirshfeld surface analysis and is discussed in terms of polar and nonpolar regions.