Charge-Scaling Effect in Ionic Liquids from the Charge-Density Analysis of N, N'-Dimethylimidazolium Methylsulfate

The charge scaling effect in ionic liquids was explored on the basis of experimental and theoretical charge-density analyses of [C1MIM][C1SO4] employing the quantum theory of atoms in molecules (QTAIM) approach. Integrated QTAIM charges of the experimental (calculated) charge density of the cation and anion resulted in non-integer values of +/- 0.90 (+/- 0.87)e. Efficient charge transfer along the bond paths of the hydrogen bonds between the imidazolium ring and the anion was considered as the origin of these reduced charges. In addition, a detailed QTAIM analysis of the bonding situation in the [C1SO4](-) anion revealed the presence of negative (O)sigma*(S-O) hyperconjugation.