Gas-phase electronic properties of tri-cationic imidazolium-based ionic liquids in comparison with mono- and di-cationic ionic liquids.

The optimized geometries, electronic structures, and gas-phase properties of widely applicable non-linear trigeminal tri-cationic ILs (TT-X) were investigated using density functional theory (DFT) calculations and compared with mono- (M-X) and di-cationic (D-X) ionic liquids. The studied ILs are based on the imidazolium cation containing halide (X) anions, where X = Cl, Br and I. Inter-molecular hydrogen bonds were studied by atoms in molecules (AIM) and natural bond orbital (NBO) analyses. Accordingly the most significant cation-anion charge transfer is related to C-H … X (X = Cl, Br, I) interaction which strongly occurs in TT-X ILs and especially in TT-Cl. Among ILs under investigation, TT-Cl has the strongest cation-anion interaction. Also M - I IL has the largest and D-Cl has the smallest electrical dipole moment.