Endohedral gas adsorption by cucurbit[7]uril: a theoretical study.

The selectivity of cucurbit[7]uril (CB[7]) towards adsorbing a series of 14 molecules encompassing four hydrocarbons (C2H2, C2H4, C2H6, and CH4), diatomic molecules of halogens (F2 and Cl2), nitrogen oxides (NO2 and NO), carbon oxides (CO2 and CO), SO2, H2S, N2, and H2 is explored via a density functional theory based study. CB[7] is noted to have high selectivity towards adsorbing SO2 over the other considered molecules, highlighting its probable utility to separate SO2 from flue gas or other gas mixtures containing these molecules. The nature of bonding is deciphered via the computations of non-covalent interaction indices and energy decomposition analysis. Although in all cases the dispersion interaction turns out to be the most dominating contributor in stabilizing these complexes, the electrostatic contribution is also considerable. In fact, the combined effect of these two energy terms in SO2@CB[7] is responsible for the obtained selectivity.