Crystallographic analysis of CO 2 sorption state in seemingly nonporous molecular crystal of azacalix[4]arene tetramethyl ether exhibiting highly selective CO 2 uptake

Described are the crystal structures and solid–gas sorption behaviors of azacalix[4]arene tetramethyl ether at low temperatures. Single crystals of the azacalix[4]arene with a seemingly nonporous crystal architecture exhibited highly selective uptake of CO2 among five examined gases such as N2, O2, Ar, CO2, and CH4. Single crystal X-ray crystallographic analysis successfully visualized the CO2 sorption state in which the azacalix[4]arene contacted with CO2 through intermolecular CH/O-interactions. A combination of the experimental results and theoretical calculations on the CO2 sorption state demonstrated that the observed high selectivity for CO2 was mainly controlled by a dispersion force, together with a molecular sieving effect.