Investigating hydrogen bonding interactions of 1-acetoxyethyl-3-methyli-midazolium bis(trifluoromethylsulfonyl)imide with various polar co-solvents

Scientific research has witnessed an increasing fascination with ester-functionalized ionic liquids in recent years. These ester-functionalized ionic liquids are particularly attractive due to their superior biodegradability and potential applications, which surpass those of traditional ionic liquids. In actual use, it is common to blend these ionic liquids with co-solvents. However, there is currently a lack of research on the structures and interaction mechanisms of these mixtures. In this work, the hydrogen bonding interactions and microstructures of 1-acetoxyethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (AOEMIMTFSI) with various polar co-solvents (DMSO, CH3OH, CH3CN) were researched by combining infrared experiments and DFT calculations. The finding are as follows: (1) O atom in [TFSI]- primary interacts with C2-H in [AOEMIM]+, while the O or N atom in the co-solvents (DMSO, CH3OH, CH3CN) primarily interact with C4,5-H in [AOEMIM]+. (2) With the addition of co-solvents (DMSO-d6, CD3OD or CD3CN), the hydrogen bonding interactions associated with the v(imidazolium C-H) in the AOEMIMTFSI- DMSO-d6/CD3OD/CD3CN systems are strengthened. (3) The hydrogen bonding interactions between AOEMIMTFSI and DMSO are the strongest, followed by those between AOEMIMTFSI and CH3OH, while the hydrogen bonding interactions between AOEMIMTFSI and CH3CN are the weakest. (4) 2[AOEMIM]+[TFSI]-, 2[AOEMIM]+[TFSI]--co-solvent, [AOEMIM]+[TFSI]--co-solvent and [AOEMIM]+-co-solvent complexes were assigned through the analysis of excess spectra.