Interaction Study Of FSI/TFSI-based Ionic Liquids With Co-solvents

Bis(fluorosulfonyl)imide([FSI]^-)and bis(trifluoromethyl)sulfonylimide([TFSI]^-)-based ionic liquids(ILs)have potential applications in electrochemistry.However,some of their mi-croscopic properties were still unclear.In this paper,the microstructure and intermolecular interactions of binary systems composed of[FSI]^-and[TFSI]^-based ILs and cosolvents were studied by combining various spectroscopic methods and quantum chemical calculation meth-ods.The hydrogen bonding interactions,C–H···?interactions,the existing form of complexes in the studied systems and the change of microstructure in the process of diluting with cosol-vent were mainly studied.Additionally,the effects of introducing a functional group,i.e.,an ether group,on the properties of the ILs were also explored.[FSI]^-and[TFSI]^-based IL–cosolvent systems used in this paper were as follows:1-methoxyethyl-3-methylimidazolium bis(fluorosulfonyl)imide(EOMIMFSI)/1-ethyl-3-me-thylimidazolium bis(fluorosulfonyl)imide(EMIMFSI)-acetonitrile(CH₃CN),1-methoxy-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide(EOMIMTFSI)-chloroform(CHCl₃)/CH₃CN/dimethyl sulfoxide(DMSO),EOMIMFSI/EOMIMTFSI-methanol(CH3OH),1-ethyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide(EMIMTFSI)/N-butylpyridinium bis(trifluoromethylsulfonyl)imide(Bpy TFSI)-toluene(C₆H₅CH₃).In the EO-MIMFSI/EMIMFSI-CH3CN systems,the hydrogen bonding interactions in the two binary systems were studied.It was found that the introduction of ether group into the cation of IL not only weakened the hydrogen bonding interaction between cation and anion/CH₃CN,but also changed the interaction site of ILs and CH₃CN.In addition,the ion clusters,small ion clusters and ion pair complexes in the two systems were identified,and their microstructure information was obtained.In the EOMIMTFSI-CHCl₃/CH3CN/DMSO systems,it was found that the hy-drogen bonding interactions of the three systems were strengthened during dilution with cosol-vents,and the hydrogen bonding strength was as follows:EOMIMTFSI-DMSO>EO-MIMTFSI-CHCl₃>EOMIMTFSI-CH₃CN.DMSO could disrupt the hydrogen bonding in-teractions between the cations and anions in EOMIMTFSI,and[EOMIM]⁺-DMSO complexes were observed in the excess infrared spectra.CHCl₃ and CH₃CN were unable to disrupt the electrostatic interactions,and only ion cluster–cosolvent and ion pair–cosolvent complexes were observed.In the EOMIMFSI/EOMIMTFSI-CH3OH systems,it was found that with the addition of CH₃OH,the hydrogen bonding interaction of the two systems were strenghened,and EOMIMFSI could form stronger hydrogen bond with CH₃OH than EOMIMTFSI.In ad-dition,some complexes were assigned to the ion cluster-CH₃OH,the ion pair-CH₃OH,and isolated ion-CH3OH complexes.In the EMIMTFSI-C₆H₅CH₃ and Bpy TFSI-C₆H₅CH₃ sys-tems,H atoms on EMIMTFSI/Bpy TFSI were located above or below the benzene ring and were mainly formed as C2–H···?bonds and C2,6–H···?bonds with C₆H₅CH₃,respectively.In the two systems,the interaction strength was as follows:EMIMTFSI-C₆H₅CH₃>Bpy TFSI-C₆H₅CH₃.Since C₆H₅CH₃ was unable to disrupt the interactions between cations and anions of ion pairs in the two systems,only ion cluster–C₆H₅CH₃ and ion pair–C₆H₅CH₃complexes were observed.