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

Author:
Jie, Kecheng, Liu, Ming, Zhou, Yujuan, Little, Marc A., Pulido, Angeles, Chong, Samantha Y., Stephenson, Andrew, Hughes, Ashlea R., Sakakibara, Fumiyasu, Ogoshi, Tomoki, Blanc, Frédéric, Day, Graeme M., Huang, Feihe, Cooper, Andrew I.
Source:
Journal of the American Chemical Society 2018 v.140 no.22 pp. 6921-6930
ISSN:
1520-5126
Subject:
X-ray diffraction, adsorption, carbon, constitutional isomers, coordination polymers, crystal structure, crystals, energy efficiency, nuclear magnetic resonance spectroscopy, solids, sorbents, stable isotopes, xylene, zeolites
Abstract:
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.
Agid:
6039008