Anion-cation interactions in novel ionic liquids based on an asymmetric sulfonimide anion observed by NMR and MD simulations

The ion interactions in two novel ionic liquids containing the a symmetric sulfonimide anion, (difluoromethanesulfonyl) (trifluoromethanesulfonyl)imide (DFTFSI), are investigated using H-1-F-19 Heteronuclear Overhauser Effect Spectroscopy (HOESY) nuclear magnetic resonance (NMR) in combination with relaxation measurements, and molecular dynamics (MD) simulations. These methods provide insights into how the different end groups of the anion interact with different regions of the IL cations. The H-1-F-19 cross-relaxation rates (s) between different pairs of nuclei measured by HOESY are interpreted based on inter/intra molecular distances and dynamics. The results show that the protonated end of the DFTFSI anion (i.e., the CF2H group) preferentially interacts with the IL cations, while the MD simulations also show evidence of C-H center dot O hydrogen bonding interactions between DFTFSI and the methoxy-functionalised cation C(2O1)mpyr, thereby explaining the observed lower ionic conductivity and higher density in this IL as compared to the C(3)mpyr DFTFSI system. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The interaction between ions in two novel ionic liquids containing DFTFSI anion was investigated, showing that the protonated end of DFTFSI preferentially interacts with IL cations. MD simulations also revealed hydrogen bonding interactions between DFTFSI and methoxy-functionalised cation, explaining the lower ionic conductivity and higher density in this IL compared to the C(3)mpyr DFTFSI system.