Rotational and Translational Dynamics of N-Butyl-N-methylpiperidinium Trifluoromethanesulfonimide Ionic Liquids Studied by NMR and MD Simulations

Abstract

Translational and rotational dynamics of the room temperature ionic liquid N-butyl-N-methylpiperidinium trifluoromethanesulfonimide, [C4mpip][Tf2N], were investigated by 1H, 19F, and 13C nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulation. 1H NMR and MD results for the temperature-dependent diffusion coefficients, D, spin–lattice relaxation times, T1, and rotational correlation times, τc, for each site in the cation of [C4mpip][Tf2N] are in good agreement. The T1 data indicate a long N–CH3 group rotation time, comparable to the overall molecular reorientation time. Correlation time comparisons between 1-butyl-3-methylimidazolium RTILs with different anions (Cl–, PF6–, Tf2N–) argue against invoking hydrogen bond interactions between the N–CH3 hydrogens and the electron rich center of the anion as an explanation of the long N–CH3 rotation times. Correlation time comparisons between piperidinium and pyrrolidinium RTILs with a common anion (Tf2N–) suggest that correlation time...