Latent porosity of planar tris(phenylisoxazolyl)benzene.

Abstract

Interest in developing separation systems for chemical entities based on crystalline molecules has provided momentum for the fabrication of synthetic porous materials showing selectivity in molecular encapsulation, such as metal-organic frameworks, covalent organic frameworks, hydrogen-bonded organic frameworks, zeolites, and macrocyclic molecular crystals. Among these, macrocyclic molecular crystals have generated renewed interest for use in separation systems. Selective encapsulation relies on the sizes, shapes, and dimensions of the pores present in the macrocyclic cavities; thus, nonmacrocyclic molecular crystals with high selectivity for molecular encapsulation via porosity-without-pore behaviors have not been studied. Here, we report that planar tris(phenylisoxazolyl)benzene forms porous molecular crystals possessing latent pores exhibiting porosity-without-pore behavior. After exposing the crystals to complementary guest molecules, the latent pores encapsulate cis- and trans-decalin while maintaining the structural rigidity responsible for the high selectivity. The encapsulation via porosity without pores is a kinetic process with remarkable selectivity for cis-decalin over trans-decalin with a cis-/trans-ratio of 96:4, which is confirmed by single-crystal X-ray diffraction and powder X-ray diffraction analyses. Hirshfeld surface analysis and fingerprint plots show that the latent intermolecular pores are rigidified by intermolecular dipole‒dipole and π-π stacking interactions, which determines the remarkable selectivity of molecular recognition.