Difference for SO2 and CO2 in TGML ionic liquids: a theoretical investigation.

Quantum chemical calculations (QM) have been used to investigate the interaction between sulfur dioxide (SO(2)) or carbon dioxide (CO(2)) molecules and ions of 1,1,3,3-tetramethylguanidium (TMG) lactate (LAC) (TMGL) ionic liquid. The QM results give us a deeper understanding of the factors that govern the high solubility of SO(2) in TMGL and the difference in the solubility of SO(2) and CO(2) in TMGL. The predicted geometries and binding energies imply a strong organization of SO(2) about the TMGL components, especially the LAC anion; but indicate a relatively weak organization of CO(2). Both the SO(2) and CO(2) molecules can interact with the TMG cations forming a N-H...O interaction; however, the binding energies demonstrate that the interaction with CO(2) is weaker than that with SO(2). The theoretical results indicate that the oxygen atoms of the LAC anion are the main active sites for the absorption of SO(2). Strong SO interactions are found for both the SO(2)-LAC and SO(2)-TMGL complexes.