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Kim, Kwang S.
Center for Superfunctional Materials (CSM)
Research Interests
  • Theoretical/experimental nanosciences, molecular electronics spectroscopy, energy materials

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High-temperature in situ crystallographic observation of reversible gas sorption in impermeable organic cages

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Title
High-temperature in situ crystallographic observation of reversible gas sorption in impermeable organic cages
Author
Baek, Seung BinMoon, DohyunGraf, RobertCho, Woo JongPark, Sung WooYoon, Tae-UngCho, Seung JooHwang, In-ChulBae, Youn-SangSpiess, Hans W.Lee, Hee CheonKim, Kwang S.
Issue Date
2015-11
Publisher
NATL ACAD SCIENCES
Citation
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, v.112, no.46, pp.14156 - 14161
Abstract
Crystallographic observation of adsorbed gas molecules is a highly difficult task due to their rapid motion. Here, we report the in situ single-crystal and synchrotron powder X-ray observations of reversible CO2 sorption processes in an apparently nonporous organic crystal under varying pressures at high temperatures. The host material is formed by hydrogen bond network between 1,3,5-tris-(4-carboxyphenyl) benzene (H3BTB) and N,N-dimethylformamide (DMF) and by pi-pi stacking between the H3BTB moieties. The material can be viewed as a well-ordered array of cages, which are tight packed with each other so that the cages are inaccessible from outside. Thus, the host is practically nonporous. Despite the absence of permanent pathways connecting the empty cages, they are permeable to CO2 at high temperatures due to thermally activated molecular gating, and the weakly confined CO2 molecules in the cages allow direct detection by in situ single-crystal X-ray diffraction at 323 K. Variable-temperature in situ synchrotron powder X-ray diffraction studies also show that the CO2 sorption is reversible and driven by temperature increase. Solid-state magic angle spinning NMR defines the interactions of CO2 with the organic framework and dynamic motion of CO2 in cages. The reversible sorption is attributed to the dynamic motion of the DMF molecules combined with the axial motions/angular fluctuations of CO2 (a series of transient opening/closing of compartments enabling CO2 molecule passage), as revealed from NMR and simulations. This temperature-driven transient molecular gating can store gaseous molecules in ordered arrays toward unique collective properties and release them for ready use
URI
https://scholarworks.unist.ac.kr/handle/201301/18008
URL
http://www.pnas.org/content/112/46/14156
DOI
10.1073/pnas.1504586112
ISSN
0027-8424
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PHY_Journal Papers
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