Crystallographic analysis of CO2sorption state in seemingly nonporous molecular crystal of azacalix[4]arene tetramethyl ether exhibiting highly selective CO2 uptake

Abstract

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.