A CUSTOM OPLS-AA FORCE FIELD FOR DICATIONIC IMIDAZOLIUM-BASED IONIC LIQUID SIMULATIONS

Xiang Zhong, Brian Doherty, and Orlando Acevedo*

Department of Chemistry, University of Miami, Coral Gables, FL 33146

Ionic liquids are a remarkable class of solvents composed exclusively of ions, characteristically at room temperature. Recently, imidazolium-based dicationic ionic liquids (DILs) have gained promising attention as a solvent medium for organic reactions, such as Claisen rearrangements, due to a broader variability in physical properties, e.g., increased thermal stability compared to 1-alkyl-3-methylimidazolium [RMIM]. This study focuses on simulations of 3,3’-(1, N-diyl)bis[1-methyl], where N=5-pentane, 6-hexane, 8-octane, 9-nonane, 10-decane, and 12-dodecane, in conjunction with the bis(trifluoromethylsulfonyl)imide [TFSI] anion. The unique sets of DIL force field parameters were developed by adapting our OPLS-2009IL force field (Sambasivarao, S. V.; Acevedo, O., J. Chem. Theory Comput. 2009, 5, 1038-1050), which was originally created for [RMIM]. Molecular dynamics simulations were performed using GROMACS for the combination of each C5-[MIM]₂, C6-[MIM]₂, C8-[MIM]₂, C9-[MIM]₂, C10-[MIM]₂, and C12-[MIM]₂ cation with the [TFSI] anion. Predictions from OPLS-2009IL DIL force field are presented for relevant solvent data that includes: densities, heats of vaporization, diffusion coefficients, and heat capacities. It has been shown for [RMIM]-based ionic liquid simulations that scaling charges improves thermodynamic properties, such as heat of vaporization, and transport properties. A scaling of ±0.8 e was also tested for the DILs.