Near-Ideal Xylene Selectivity in Adaptive Molecular Pillar[ n]arene Crystals.

The energy-efficient separation of alkylaromatic compounds is a major industrial sustainability challenge. The use of selectively porous extended frameworks, such as zeolites or metal-organic frameworks, is one solution to this problem. Here, we studied a flexible molecular material, perethylated pillar[ n]arene crystals ( n = 5, 6), which can be used to separate C8 alkylaromatic compounds. Pillar[6]arene is shown to separate para-xylene from its structural isomers, meta-xylene and ortho-xylene, with 90% specificity in the solid state. Selectivity is an intrinsic property of the pillar[6]arene host, with the flexible pillar[6]arene cavities adapting during adsorption thus enabling preferential adsorption of para-xylene in the solid state. The flexibility of pillar[6]arene as a solid sorbent is rationalized using molecular conformer searches and crystal structure prediction (CSP) combined with comprehensive characterization by X-ray diffraction and 13C solid-state NMR spectroscopy. The CSP study, which takes into account the structural variability of pillar[6]arene, breaks new ground in its own right and showcases the feasibility of applying CSP methods to understand and ultimately to predict the behavior of soft, adaptive molecular crystals.

Conversion from pillar[5]arene to pillar[6-15]arenes by ring expansion and encapsulation of C60 by pillar[n]arenes with nanosize cavities.

Conversion of ring size from pillar[5]arene to pillar[6-15]arenes and isolation of pillar[n]arene homologues (n = 11-13) with known pillar[n]arene homologues (n = 6-10) are demonstrated. Pillar[10]arene formed the most stable host-guest complex with C60 among the pillar[5-14]arenes.

The template effect of solvents on high yield synthesis, co-cyclization of pillar[6]arenes and interconversion between pillar[5]- and pillar[6]arenes.

We have synthesized a pillar[6]arene in high yield and a co-pillar[6]arene using chlorocyclohexane as a solvent.