Theoretical study on the interactions between dibenzothiophene/dibenzothiophene sulfone and ionic liquids

The interactions between sulfur-containing compounds of dibenzothiophene (DBT) and dibenzothiophene sulfone (DBTO₂) and ionic liquids of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM⁺PF₆^-) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM⁺BF₄^-) were comparatively studied by using density functional theory. The most stable structures of BMIM⁺PF₆^-, BMIM⁺PF₆^--DBT, BMIM⁺PF₆^--DBTO₂, BMIM⁺BF₄^-, BMIM⁺BF₄^--DBT, and BMIM⁺BF₄^--DBTO₂ systems were obtained by natural bond orbitals (NBO) and atoms in molecules (AIM) analyses. The results indicated that DBT and BMIM rings of BMIM⁺PF₆^-/BMIM⁺BF₄^- are parallel to each other. There is a strong π-π interaction between them in terms of NBO and AIM analyses. The H1' and H9' involved F…H hydrogen bonding interactions may favor the formation of π-π stacking interactions. The DBTO₂ preferentially locates near the C2-H2 and methyl group of BMIM⁺ to form O…H interactions. The predicted geometries and interaction energies imply the preferential adsorption of DBTO₂ on BMIM⁺PF₆^-/BMIM⁺BF₄^-. The BMIM⁺PF₆^-/BF₄^- have better extracting ability to remove DBTO₂ than DBT, possibly due to the larger polarity of DBTO₂ and stronger interactions between BMIM⁺PF₆^-/BF₄^- and DBTO₂.