Solid–gas sorption behavior of a new polymorph of azacalix[5]arene pentamethyl ether as controlled by crystal architecture

Abstract

Described are the crystal structure and solid–gas sorption behavior of a new polymorph of azacalix[5]arene 2. Single crystals of the benzene clathrate of 2 tolerated guest removal and furnished a solvent-free crystalline powder material 2PB that was in a polymorphic relationship with our previously studied crystalline powder 2PD. A newly prepared polymorph 2PB was nonporous to all of the examined gases, whereas 2PD exhibited the selective uptake of CO₂ under ambient temperature and pressure conditions. Ab initio powder X-ray diffraction analysis and potential energy distribution analysis revealed that a difference in the crystal architecture of 2PB and 2PD played a critical role in defining the potential energy distribution in the crystals and hence controlling the solid–gas sorption behavior.