Comparative study of the hydrogen bonding properties between bis(fluorosulfonyl)imide/bis(trifluoromethyl)sulfonylimide-based ether-functionalized ionic liquids and methanol

Abstract

Bis(fluorosulfonyl)imide ([FSI]−) and bis(trifluoromethyl)sulfonylimide ([TFSI]−)-based ionic liquids have potential applications in electrochemistry. However, some fundamental questions regarding their hydrogen bonding properties remain to be answered. In this work, the hydrogen bonding interactions between two [FSI]− and [TFSI]−-based ionic liquids and methanol (CH3OH) and their microscopic structure were comparatively investigated by infrared spectroscopy, excess spectroscopy and quantum chemical calculations. Some conclusions can be drawn: (1) The hydrogen bonding interactions in the two systems are strengthened with the addition of CH3OH. Moreover, EOMIMFSI ([EOMIM]+, 1-methoxyethyl-3-methylimidazolium) can form stronger hydrogen bonds with CH3OH than EOMIMTFSI. (2) The excess peaks of v(O–H), v(aromatic C–Hs) and vas(S=O) show fixed positive and negative excess peaks, indicating distinct complexes. With combination of the excess spectra and quantum chemical calculations, the newly formed distinct complexes were assigned to the ion cluster-CH3OH, the ion pair-CH3OH, and isolated ion-CH3OH complexes. The microscopic structure of the two systems was also shown with dilution. (3) The C4–H in EOMIMFSI is the main interaction site interacting with CH3OH, while the C2–H in EOMIMTFSI is the main interaction site.