Highly selective carbon dioxide sorption in an organic molecular porous material

The organic molecular porous material 1 obtained by recrystallization of cucurbit[6]uril (CB[6]) from HCl shows a high CO₂ sorption capacity at 298 K, 1 bar. Most interestingly, 1 showed the highest selectivity of CO ₂ over CO among the known porous materials so far. The remarkable selectivity of CO₂ may be attributed to the exceptionally high enthalpy of adsorption (33.0 kJ/mol). X-ray crystal structure analysis of CO₂ adsorbed 1 revealed three independent CO₂ sorption sites: two in the 1D channels (A and B) and one in the molecular cavities (C). The CO₂ molecules adsorbed at sorption site A near the wall of the 1D channels interact with 1 through hydrogen bonding and at the same time interact with those at site B mainly through quadrupolequadrupole interaction in a T-shaped arrangement. Interestingly, two CO₂ molecules are included in the CB[6] cavity (site C), interacting not only with the carbonyl groups of CB[6] but also with each other in a slipped-parallel geometry. The exceptionally selective CO₂ sorption properties of 1 may find useful applications in the pressure swing adsorption (PSA) process for CO₂ separation not only in the steel industry but also in other industries such as natural gas mining.