Robust Fluorine-Decorated {Yb<sub>4</sub>}-Organic Framework for C<sub>2</sub>H<sub>6</sub> Capture and Efficient Catalytic Performance on CO<sub>2</sub>-Epoxide Cycloaddition
Zhenfeng Wang, Yang Fei, Aimiao Qin, Shu‐Hua Zhang, Xiutang Zhang
Abstract
Fluorine-functionalized MOFs have excellent unusual properties such as gas adsorption and separation and catalysis, but the functionalization of existing ligands and the self-assembly of functionalized MOFs remain a challenge. Herein, we report a robust fluorine-functionalized nanochannel-based ytterbium(III)-organic framework of {(Me 2 NH 2 )[Yb 4 (CFPDA) 2 (μ 2 -HCO 2 )(μ 3 -OH) 2 (H 2 O) 2 ]·4DMF·5H 2 O} n ( NUC-122, H 5 CFPDA = 4,4′-(4-(4-carboxy-2-fluorophenyl)pyridine-2,6-diyl)diisophthalic acid) with [Yb 4 (μ 3 -OH) 2 (μ 2 -HCO 2 )(H 2 O) 2 ] clusters as secondary building units (SBUs). Compared to reported anionic skeleton of [Yb 4 (BDCP) 2 (μ 2 -HCO 2 )(μ 3 -OH) 2 (H 2 O) 2 ] n ( NUC-38Yb ), the void volume of NUC-122 (54.1%) is slightly lower than that of NUC-38Yb (56.7%), which is caused by functionalized fluorine atoms on the ligand of H 5 BDCP. Because of the introduction of fluorine groups, activated NUC-122a displays a higher adsorption capacity for CO 2 along with the value of 117.5 cm 3 /g (273 K) and 63.1 cm 3 /g (298 K). Further, activated NUC-122a has a high ethane (C 2 H 6 ) separation performance over the mixture of C 2 H 6 /C 2 H 4 with the selectivity of 1.6, enabling the purity of recycled C 2 H 4 to reach 99.99%. Moreover, the CO 2 -epoxide cycloaddition could be efficiently catalyzed by NUC-122a under comparatively mild conditions. Under optimal catalytic conditions of 0.13 mol % MOFs, 1.69 mol % n -Bu 4 NBr, 0.7 MPa CO 2, 70 °C, and 3 h, the conversion yield of SO to SC catalyzed by NUC-122a is 26% higher than that catalyzed by NUC-38Yb . The excellent separation and catalytic performance should be attributed to the combined diverse functional groups such as Lewis acidic sites of Yb 3+, Lewis basic sites of −F and N pyridine atoms, and electrophilic H-bond donors (HBD) of μ 3 –OH and μ 2 -HCO 2 moieties. Hence, this work not only reports a fluorine-functionalized multifunctional material but also provides an in-depth insight into the synthetic strategy of functionalized metal–organic host frameworks.