title: High-temperature in situ crystallographic observation of reversible gas sorption in impermeable organic cages.
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 π-π 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.
authors.affiliation: Department of Chemistry and Center for Superfunctional Materials, Ulsan National Institute of Science and Technology, Ulsan 689-798, Korea;
authors.forename: Seung Bin
authors.initials: SB
authors.lastname: Baek
authors.affiliation: Pohang Accelerator Laboratory, Pohang 790-834, Korea;
authors.forename: Dohyun
authors.initials: D
authors.lastname: Moon
authors.affiliation: Max-Planck-Institute for Polymer Research, 55128, Mainz, Germany;
authors.forename: Robert
authors.initials: R
authors.lastname: Graf
authors.affiliation: Department of Chemistry and Center for Superfunctional Materials, Ulsan National Institute of Science and Technology, Ulsan 689-798, Korea;
authors.forename: Woo Jong
authors.initials: WJ
authors.lastname: Cho
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea;
authors.forename: Sung Woo
authors.initials: SW
authors.lastname: Park
authors.affiliation: Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 120-749, Korea;
authors.forename: Tae-Ung
authors.initials: TU
authors.lastname: Yoon
authors.affiliation: Department of Cellular Molecular Medicine, College of Medicine, Chosun University, Gwangju 501-759, Korea.
authors.forename: Seung Joo
authors.initials: SJ
authors.lastname: Cho
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea;
authors.forename: In-Chul
authors.initials: IC
authors.lastname: Hwang
authors.affiliation: Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 120-749, Korea;
authors.forename: Youn-Sang
authors.initials: YS
authors.lastname: Bae
authors.affiliation: Max-Planck-Institute for Polymer Research, 55128, Mainz, Germany;
authors.forename: Hans W
authors.initials: HW
authors.lastname: Spiess
authors.affiliation: Department of Chemistry, Pohang University of Science and Technology, Pohang 790-784, Korea;
authors.forename: Hee Cheon
authors.initials: HC
authors.lastname: Lee
authors.affiliation: Department of Chemistry and Center for Superfunctional Materials, Ulsan National Institute of Science and Technology, Ulsan 689-798, Korea; kimks@unist.ac.kr.
authors.forename: Kwang S
authors.initials: KS
authors.lastname: Kim
keywords: CO2 sorption; in situ X-ray diffraction; nonporous organic crystalline material