Combining In Situ Techniques (XRD, IR, and (13)C NMR) and Gas Adsorption Measurements Reveals CO(2)-Induced Structural Transitions and High CO(2)/CH(4) Selectivity for a Flexible Metal–Organic Framework JUK-8

[Image: see text] Flexible metal–organic frameworks (MOFs) are promising materials in gas-related technologies. Adjusting the material to processes requires understanding of the flexibility mechanism and its influence on the adsorption properties. Herein, we present the mechanistic understanding of CO(2)-induced pore-opening transitions of the water-stable MOF JUK-8 ([Zn(oba)(pip)](n), oba(2–) = 4,4′-oxybis(benzenedicarboxylate), pip = 4-pyridyl-functionalized benzene-1,3-dicarbohydrazide) as well as its potential applicability in gas purification. Detailed insights into the global structural transformation and subtle local MOF–adsorbate interactions are obtained by three in situ techniques (XRD, IR, and (13)CO(2)-NMR). These results are further supported by single-crystal X-ray diffraction (SC-XRD) analysis of the solvated and guest-free phases. High selectivity toward carbon dioxide derived from the single-gas adsorption experiments of CO(2) (195 and 298 K), Ar (84 K), O(2) (90 K)(,) N(2) (77 K), and CH(4) (298 K) is confirmed by high-pressure coadsorption experiments of the CO(2)/CH(4) (75:25 v/v) mixture at different temperatures (288, 293, and 298 K) and in situ NMR studies of the coadsorption of (13)CO(2)/(13)CH(4) (50:50 v/v; 195 K).