Isoreticular Contraction of Cage-like Metal-Organic Frameworks with Optimized Pore Space for Enhanced C2H2/CO2 and C2H2/C2H4 Separations.

The C2H2 separation from CO2 and C2H4 is of great importance yet highly challenging in the petrochemical industry, owing to their similar physical and chemical properties. Herein, the pore nanospace engineering of cage-like mixed-ligand MFOF-1 has been accomplished via contracting the size of the pyridine- and carboxylic acid-functionalized linkers and introducing a fluoride- and sulfate-bridging cobalt cluster, based on a reticular chemistry strategy. Compared with the prototypical MFOF-1, the constructed FJUT-1 with the same topology presents significantly improved C2H2 adsorption capacity, and selective C2H2 separation performance due to the reduced cage cavity size, functionalized pore surface, and appropriate pore volume. The introduction of fluoride- and sulfate-bridging cubane-type tetranuclear cobalt clusters bestows FJUT-1 with exceptional chemical stability under harsh conditions while providing multiple potential C2H2 binding sites, thus rendering the adequate ability for practical C2H2 separation application as confirmed by the dynamic breakthrough experiments under dry and humid conditions. Additionally, the distinct binding mechanism is suggested by theoretical calculations in which the multiple supramolecular interactions involving C-H···O, C-H···F, and other van der Waals forces play a critical role in the selective C2H2 separation.

Optimized Pore Nanospace through the Construction of a Cagelike Metal-Organic Framework for CO2/N2 Separation.

The development of metal-organic framework (MOF) adsorbents with a potential molecule sieving effect for CO2 capture and separation from flue gas is of critical importance for reducing the CO2 emissions to the atmosphere yet challenging. Herein, a cagelike MOF with a suitable cage window size falling between CO2 and N2 and the cavity has been constructed to evaluate its CO2/N2 separation performance. It is noteworthy that the introduction of coordinated dimethylamine (DMA) and N,N'-dimethylformamide (DMF) molecules not only significantly reduces the cage window size but also enhances the framework-CO2 interaction via C-H···O hydrogen bonds, as proven by molecular modeling, thus leading to an improved CO2 separation performance. Moreover, transient breakthrough experiments corroborate the efficient CO2/N2 separation, revealing that the introduction of DMA and DMF molecules plays a vital role in the separation of a CO2/N2 gas mixture.