The comparative study on interactions between ionic liquid and CO2/SO2 by a hybrid density functional approach in the gas phase

By using hybrid density functional calculations, we have carried out theoretical studies of the interactions between 1-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]) ionic liquid and CO2/SO2. The interacting structures between [BMIM][MeSO4] and CO2/SO2 are significantly different. The optimized structure of [BMIM][MeSO4]-CO2 demonstrates that the dominant interaction between CO2 and [BMIM][MeSO4] is LP(O29) → π*(C35O36). While the strong interactions between SO2 and [BMIM][MeSO4] are LP(O36) → σ*(C3H12), LP(O36) → σ*(C4H13), and LP(O28) → π*(S35O37). The most dominant interaction between SO2 and [BMIM][MeSO4] is LP(O28) → π*(S35O37), with the electrons mainly migration from the highest occupied molecular orbital (HOMO) of [MeSO4]− anion to the lowest unoccupied molecular orbital (LUMO) of SO2. The interaction energy between [BMIM][MeSO4] and SO2 is larger than that between [BMIM][MeSO4] and CO2. The imidazolium ring of [BMIM][MeSO4] is more aromatic than that of [BMIM][MeSO4]SO2, but less aromatic than that of [BMIM][MeSO4]CO2. CO2 acts as an electron donor when it interacts with [BMIM][MeSO4], while SO2 is an electron acceptor when it interacts with [BMIM][MeSO4].