Ether-Functionalized Pyrrolidinium-Based Room Temperature Ionic Liquids: Physicochemical Properties, Molecular Dynamics, and the Lithium Ion Coordination Environment.

The physicochemical properties of room temperature ionic liquids (RTILs) consisting of bis(trifluoromethanesulfonyl)amide (TFSA- ) combined with 1-hexyl-1-methylpyrrolidinium (Pyr1,6 + ), 1-(butoxymethyl)-1-methylpyrrolidinium (Pyr1,1O4 + ), 1-(4-methoxybutyl)-1-methyl pyrrolidinium (Pyr1,4O1 + ), and 1-((2-methoxyethoxy)methyl)-1-methylpyrrolidinium (Pyr1,1O2O1 + ) were investigated using both experimental and computational approaches. Pyr1,1O2O1 TFSA, which contains two ether oxygen atoms, showed the lowest viscosity, and the relationship between its physicochemical properties and the position and number of the ether oxygen atoms was discussed by a careful comparison with Pyr1,1O4 TFSA and Pyr1,4O1 TFSA. Ab initio calculations revealed the conformational flexibility of the side chain containing the ether oxygen atoms. In addition, molecular dynamics (MD) calculations suggested that the ion distributions have a significant impact on the transport properties. Furthermore, the coordination environments of the Li ions in the RTILs were evaluated using Raman spectroscopy, which was supported by MD calculations using 1000 ion pairs. The presented results will be valuable for the design of functionalized RTILs for various applications.