Abstract
Covalent organic frameworks (COFs) are emerging crystalline porous polymers, showing great potential for applications but lacking gas-triggered flexibility. Atropisomerism was experimentally discovered in 1922 but has rarely been found in crystals with infinite framework structures. Here we report atropisomerism in COF single crystals. The obtained COF atropisomers, namely COF-320 and COF-320-A, have identical chemical and interpenetrated structures but differ in the spatial arrangement of repeating units. In contrast to the rigid COF-320 structure, its atropisomer (COF-320-A) exhibits unconventional gas sorption behaviours with one or more sorption steps in isotherms at different temperatures. Single-crystal structures determined from continuous rotation electron diffraction and in situ powder X-ray diffraction demonstrate that these adsorption steps originate from internal pore expansion with or without changing the crystal space group. COF-320-A recognizes different gases by expanding its internal pores continuously (crystal-to-amorphous transition) or discontinuously (crystal-to-crystal transition) or having mixed transition styles, distinguishing COF-320-A from existing soft/flexible porous crystals. These findings extend atropisomerism from molecules to crystals and propel COFs into the covalently linked soft porous crystal regime, further advancing applications of soft porous crystals in gas sorption, separation and storage.
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Data availability
All data are available in the main text or the Supplementary Information. The crystallographic data for single-crystal COF-320-A and COF-320-A2 have been deposited at the Cambridge Crystallographic Data Centre (CCDC, free of charge at https://www.ccdc.cam.ac.uk) under deposition numbers CCDC 2111901 and 2111902, respectively. Correspondence and requests for materials should be addressed to the corresponding authors.
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Acknowledgements
This work was supported by ExxonMobil through the Singapore Energy Center (EM11161.TO4, EM11161.TO17), the Ministry of Education—Singapore (MOE2019-T2-1-093, MOE-T2EP10122-0002), the Energy Market Authority of Singapore (EMA-EP009-SEGC-020), the Agency for Science, Technology and Research (U2102d2004, U2102d2012), the National Research Foundation Singapore (NRF-CRP26-2021RS-0002), Japan Society for the Promotion of Science KAKENHI (JP19H02734, JP20H02575, JP20K20564), the Swedish Research Council (VR, 2016-04625; 2017-04321) and the Swedish Research Council Formas (2020-00831). We thank the staff from the test centre of the Department of Chemical and Biomolecular Engineering, National University of Singapore, for the assistance with scanning electron microscopy and Fourier-transform infrared spectroscopy measurements.
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Contributions
D.Z. formulated and supervised the project. C.K. performed the synthesis of COF-320-A crystals and analyses of its growth kinetics and gas sorption measurements. Z.Z. and C.K. performed simulations on the COF–gas interactions. S.K., K.N. and R.M. performed in situ PXRD measurements. Z.H. and X.Z. performed the structure resolving of COF-320-A and COF-320-A2 single crystals. C.K. and D.Z. wrote the manuscript. A.K.U., D.C.C., L.S.B., Y.W., Z.Z., S.K., K.N., X.Z., Z.H., and R.K. contributed to the data analysis, discussion and manuscript revision.
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Nature Materials thanks François-Xavier Coudert and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Supplementary information
Supplementary Information
Supplementary Figs. 1–18 and Tables 1–7.
Supplementary Data 1
Crystal structure of COF-320-A.
Supplementary Data 2
Crystal structure of COF-320-A2.
Supplementary Data 3
Simulated and refined atomistic coordinates of COF-320-A2 during C2H4 adsorption.
Supplementary Data 4
Simulated and refined atomistic coordinates of COF-320-A2E1 during C2H4 adsorption.
Supplementary Data 5
Simulated and refined atomistic coordinates of COF-320-AE1 during CO2 adsorption.
Supplementary Data 6
Simulated and refined atomistic coordinates of COF-320-AE2 during CO2 adsorption.
Supplementary Data 7
Simulated and refined atomistic coordinates of COF-320-AE3 during CO2 adsorption.
Supplementary Data 8
Simulated and refined atomistic coordinates of COF-320-A2E2 during C2H2 adsorption.
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Kang, C., Zhang, Z., Kusaka, S. et al. Covalent organic framework atropisomers with multiple gas-triggered structural flexibilities. Nat. Mater. 22, 636–643 (2023). https://doi.org/10.1038/s41563-023-01523-2
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DOI: https://doi.org/10.1038/s41563-023-01523-2