Structures and hydrogen bonding investigation of 1,3-dimethylimidazolium methylsulfate and 1,3-dimethylimidazolium dimethylphosphate with theoretical methods

The structures and H-bonds for 1,3-dimethylimidazolium methylsulfate ([DMIM][MS]) and 1,3-dimethylimidazolium dimethylphosphate ([DMIM][DMP]) have been investigated with density functional theory (DFT) method. The optimized geometries of for each ion pair as well as their ion pair dimer are identified by analyzing the relative self-consistent field (SCF) energies. The results show that the major intermolecular interaction in the ion pairs and their clusters is multiple C–H⋯O type H-bond. Atoms in molecules (AIM) theory and natural bond orbital (NBO) analysis are employed for the complexes under study, to gain a deeper understanding of the detail of these hydrogen bonding interactions. In addition, the results of energy decomposition analysis (EDA) show that the interaction of these anions with cation is electrostatic in the nature.