Investigation of 1,2,3-trialkylimidazolium ionic liquids: experiment and density functional theory calculations

Physico-chemical properties, thermal stability and bonding in 1,2,3-trialkylimidazolium based ionic liquids (ILs) were investigated by viscosity and density measurements together with thermogravimetric analysis (TGA) and IR spectroscopy. The obtained results were compared to those obtained for the corresponding 1,3-dialkylimidazolium based ILs. To obtain more insight into the influence of the methylation at position C-2 of the imidazolium ion, IR spectra were calculated with the help of density functional theory (DFT) calculations. The reduction in bonding intensity between ions was confirmed as a consequence of chain reduction and methylation. In this regard, DFT calculations indicated a much higher influence of methylation and these results were explained through the analysis of inter-molecular non-covalent interactions (NCIs). Intra-molecular NCIs together with quantum molecular descriptors were also applied for the explanation of thermal stability of the investigated ILs.