Robust Fluorine-Decorated {Yb4}-Organic Framework for C2H6 Capture and Efficient Catalytic Performance on CO2-Epoxide Cycloaddition

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 {(Me2NH2)[Yb4(CFPDA)2(μ2-HCO2)(μ3-OH)2(H2O)2]·4DMF·5H2O}n (NUC-122, H5CFPDA = 4,4'-(4-(4-carboxy-2-fluorophenyl)pyridine-2,6-diyl)diisophthalic acid) with [Yb4(μ3-OH)2(μ2-HCO2)(H2O)2] clusters as secondary building units (SBUs). Compared to reported anionic skeleton of [Yb4(BDCP)2(μ2-HCO2)(μ3-OH)2(H2O)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 H5BDCP. Because of the introduction of fluorine groups, activated NUC-122a displays a higher adsorption capacity for CO2 along with the value of 117.5 cm3/g (273 K) and 63.1 cm3/g (298 K). Further, activated NUC-122a has a high ethane (C2H6) separation performance over the mixture of C2H6/C2H4 with the selectivity of 1.6, enabling the purity of recycled C2H4 to reach 99.99%. Moreover, the CO2-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-Bu4NBr, 0.7 MPa CO2, 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 Yb3+, Lewis basic sites of -F and Npyridine atoms, and electrophilic H-bond donors (HBD) of μ3-OH and μ2-HCO2 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.