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The development of porous MOFs exhibiting highly selective C2H2/CH4 and CO2/CH4 separations is quite important to meet the requirement of high-purity C2H2 and CH4 in various industries. By employing a ligand heterobifunctionalization strategy, we designed and synthesized an aminopyridine-functionalized diisophthalate ligand, and successfully targeted its corresponding copper-based NbO-type MOF ZJNU-98. Gas adsorption studies revealed that ZJNU-98 exhibited significantly enhanced adsorption of C2H2 and CO2 over CH4 compared to its parent MOF, NOTT-101. At 298 K and 1 atm, C2H2 and CO2 uptakes of ZJNU-98 are 10.0% and 16.7% higher than the corresponding values of NOTT-101, while 14.2% and 18.8% increases in C2H2/CH4 and CO2/CH4 adsorption selectivities were observed for the equimolar gas mixtures in ZJNU-98 compared to NOTT-101. Furthermore, the contribution of the functional group effect on gas adsorption has been assessed, demonstrating that the amine group plays a more important role than the pyridinic-N atom despite its lower Lewis basicity. This work provided an effective way and significant experimental evidence for the design of new porous MOFs with highly enhanced gas adsorption performance.

The development of porous MOFs with novel structures and functional properties is a key research topic in the MOF chemistry and materials field. In this article, by employing a ligand conformation preorganization strategy, we designed a nonplanar methyl-substituted triisophthalate ligand, which was used to successfully construct a copper–hexacarboxylate framework with a novel topological structure. More importantly, the obtained MOF not only exhibits good hydrolytic stability but also shows utility as an adsorbent for efficient separation and purification of C2H2 and natural gas under ambient conditions. At ambient temperature and atmospheric pressure, the C2H2 and CO2 uptake capacities reach up to 149.1 and 83.1 cm3 (STP) g−1, while the IAST-predicted C2H2/CH4 (50/50, v/v), C2H2/CO2 (50/50, v/v), and CO2/CH4 (50/50, v/v) adsorption selectivities are as high as 22.2, 3.81, and 5.13.

NbO-type MOFs constructed from dicopper paddlewheel secondary building units and diisophthalate ligands not only exhibit great promise for the separation of environment and energy-related gas pairs but also more importantly provide an excellent platform for the fundamental investigation of structure–property relationships. In this work, two NbO-type MOFs (ZJNU-91 and ZJNU-92) derived from linear and zigzag-shaped thieno[3,2-b]thiophene-functionalized diisophthalate ligands were solvothermally prepared and structurally characterized. Their gas adsorption properties with respect to C2H2, CO2, and CH4 were systematically investigated, revealing that they exhibit promising potential for selective adsorptive separation of C2H2–CH4 and CO2–CH4 binary gas mixtures which are associated with acetylene production and natural gas upgrading. In particular, compared to its isomer ZJNU-92, ZJNU-91 displays larger C2H2 and CO2 uptake capacities as well as higher C2H2/CH4 and CO2/CH4 adsorption selectivities under ambient conditions, despite its lower surface area and pore volume. On the basis of structural analyses, the better performance of ZJNU-91 compared to its isomer ZJNU-92 can be ascribed to its more optimized pore size.

Understanding the structure–property relationship is conducive to the rational design and synthesis of porous MOFs with better performance. In this work, we constructed three isoreticular MOFs derived from quinoline-functionalized bent diisophthalate ligands as a platform to investigate the positional effect of nitrogen functional sites on the structural stabilities and gas adsorption properties of the resulting MOFs. N2 adsorption experiments performed at 77 K revealed that the three MOF compounds exhibited different stabilities against the framework desolvation, which we think is attributed to different accessibility degrees of nitrogen functional sites leading to different interactions between the frameworks and activated solvent molecules. In addition, as a consequence of the incorporation of nitrogen functional sites into the framework, the most stable MOF ZJNU-84 outperformed its parent compound ZJNU-71 in terms of C2H2 and CO2 uptake capacities and C2H2/CH4 and CO2/CH4 adsorption selectivities, indicating its promising potential for the selective separation of C2H2 and CO2 from CH4. However, the enhancement is not as remarkable as expected due to a low degree of accessibility of nitrogen functional sites in the framework.

Solvothermal reactions of cyclotriphosphazene-functionalized hexacarboxylate derivatives bearing different substituents (methoxy, chloro, bromo and methyl) with Ho(NO3)3·6H2O gave rise to four new three-dimensional lanthanide metal–organic frameworks (Ln-MOFs). Single-crystal X-ray diffraction analyses reveal that they all feature rod-shaped Ho-carboxylate chains as inorganic secondary building units but display substituent-driven structural diversities instead of the isoreticular structures. N2 adsorption and desorption studies show that among these Ln-MOFs, only the methoxy-modified Ln-MOF ZJNU-63 after activation exhibits permanent porosity. Furthermore, the gas adsorption properties of ZJNU-63 with respect to C2H2, C2H4, C2H6, CO2, and CH4 were systematically investigated, revealing its possible potential for natural gas purification. Although the separation performance is not very impressive compared to the other reported MOFs, ZJNU-63 presents a rare example of permanently porous Ln-MOFs constructed from flexible organic ligands displaying selective gas adsorption. Besides, ZJNU-63 can adsorb a large amount of C4 hydrocarbons with uptake capacities ranging from 58.8 to 75.7 cm3 (STP) g−1 at 298 K and 1 atm.