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 ( SO2) or carbon dioxide ( CO2) 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 SO2 in TMGL and the difference in the solubility of SO2 and CO2 in TMGL. The predicted geometries and binding energies imply a strong organization of SO2 about the TMGL components, especially the LAC anion; but indicate a relatively weak organization of CO2. Both the SO2 and CO2 molecules can interact with the TMG cations forming a N-H...O interaction; however, the binding energies demonstrate that the interaction with CO2 is weaker than that with SO2. The theoretical results indicate that the oxygen atoms of the LAC anion are the main active sites for the absorption of SO2. Strong S...O interactions are found for both the SO2-LAC and SO2-TMGL complexes.