Crossover Sorption of C2H2/CO2 and C2H6/C2H4 in Soft Porous Coordination Networks |
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Authors: | Mohana Shivanna Ken-ichi Otake Shotaro Hiraide Takao Fujikawa Ping Wang Yifan Gu Hirotaka Ashitani Shogo Kawaguchi Yoshiki Kubota Minoru T. Miyahara Susumu Kitagawa |
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Affiliation: | 1. Institute for Integrated Cell-Material Sciences, Kyoto University Institute for Advanced Study, Kyoto University Yoshida Ushinomiya-cho, Sakyo-ku, Kyoto, 606-8501 Japan;2. Department of Chemical Engineering, Kyoto University Nishikyo, Kyoto, 615-8510 Japan;3. Department of Physical Science, Graduate School of Science, Osaka Prefecture, University, Sakai, Osaka, 599-8531 Japan Japan Synchrotron Radiation Research Institute (JASRI), SPring-8, 1–1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198 Japan;4. Japan Synchrotron Radiation Research Institute (JASRI), SPring-8, 1–1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo, 679-5198 Japan;5. Department of Physical Science, Graduate School of Science, Osaka Prefecture, University, Sakai, Osaka, 599-8531 Japan |
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Abstract: | Porous sorbents are materials that are used for various applications, including storage and separation. Typically, the uptake of a single gas by a sorbent decreases with temperature, but the relative affinity for two similar gases does not change. However, in this study, we report a rare example of “crossover sorption,” in which the uptake capacity and apparent affinity for two similar gases reverse at different temperatures. We synthesized two soft porous coordination polymers (PCPs), [Zn2(L1)(L2)2]n (PCP-1) and [Zn2(L1)(L3)2]n (PCP-2) (L1= 1,4-bis(4-pyridyl)benzene, L2=5-methyl-1,3-di(4-carboxyphenyl)benzene, and L3=5-methoxy-1,3-di(4-carboxyphenyl)benzene). These PCPs exhibits structural changes upon gas sorption and show the crossover sorption for both C2H2/CO2 and C2H6/C2H4, in which the apparent affinity reverse with temperature. We used in situ gas-loading single-crystal X-ray diffraction (SCXRD) analysis to reveal the guest inclusion structures of PCP-1 for C2H2, CO2, C2H6, and C2H4 gases at various temperatures. Interestingly, we observed three-step single-crystal to single-crystal (sc-sc) transformations with the different loading phases under these gases, providing insight into guest binding positions, nature of host–guest or guest-guest interactions, and their phase transformations upon exposure to these gases. Combining with theoretical investigation, we have fully elucidated the crossover sorption in the flexible coordination networks, which involves a reversal of apparent affinity and uptake of similar gases at different temperatures. We discovered that this behaviour can be explained by the delicate balance between guest binding and host–guest and guest-guest interactions. |
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Keywords: | C2H2/CO2 and C2H6/C2H4 Sorption Crossover Sorption Flexibility In-Situ Characterization Porous Coordination Polymer |
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