Synthesis and characterization of dicationic and monocationic fluorine-containing DBU based ionic liquids: Experimental and quantum chemical approaches

•DBU based dicationic and monocationic ionic liquids were synthesized and characterized.•Thermal stability of DBU based ionic liquids was determined.•Structural properties of DBU based ionic liquids were studied.•Interaction energy in DBU based ionic liquids was explored. In this study, the new dication ionic liquids (DILs) based on para-xylyl linked bis-1,8-diazobicyclo [5.4.0] undec-7-ene ([p-C6H4(CH2DBU)2]2+) dication and their corresponding monocation ionic liquids (MILs) containing the bis(trifluoromethanesulfonyl) imide [NTf2]− and trifluoromethanesulfonate [OTF]− anions are synthesized. The method is based on the functionalization reaction of DBU salts using a simple procedure under microwave irradiation, followed by anion exchange. The obtained ILs are characterized by 1H-NMR, 13C-NMR, and FT-IR spectroscopy. The thermal decomposition of [p-C6H4(CH2DBU)2][NTf2]2, [p-C6H4(CH2DBU)2][OTF]2, [C6H5−CH2DBU][NTf2] and [C6H5−CH2DBU][OTF] ILs are measured using thermogravimetric (TGA) analyses and differential scanning calorimetry (DSC) in the temperature range from 25 to 800 °C. The thermal behavior confirmed that the DILs and MILs including [NTf2]− are more stable than the DILs and MILs including [OTF]− that is in good agreement with the greater dispersion energy calculated for [NTf2]− based ILs. The [p-C6H4(CH2DBU)2][NTf2]2 DIL shows good thermal stability up to 435°C which makes them suitable for thermal application. Finally, the cation-anion interactions were investigated in both DILs and MILs using DFT-M06-2X functional in conjunction with the 6-311++G(d,p) basis set. The results indicate that hydrogen bonding is stronger in the IL containing [OTF]− anion. The calculations in the solution phase with COSMO-RS method show that the ILs including [OTF]− anion have greater solvation energy and for the DILs are larger than those of MILs.