Molecular Handle-Driven Gate-Opening in Isoreticular Metal-Organic Frameworks Enables Efficient Separation of Light...

The separation of light hydrocarbons with similar molecular structures, such as ethane and propane, remains a critical challenge in natural gas purification since propane interacts over strongly with the polar sites of adsorbents, which in turn suppresses ethane adsorption and reduces the yield of high-purity methane consequently. Here, we report the rational design of two isoreticular Zn-based metal-organic frameworks (Zn-fum-DAT and Zn-mes-DAT) with tunable pore environments achieved through molecular handle engineering. Utilizing fumaric and mesaconic acids as pillars, respectively, these MOFs feature distinct aliphatic pore architectures stabilized by hydrogen-bonding networks between carboxylate pillars and the diamino-triazole (DAT) ligand. The methyl handles in Zn-mes-DAT can be selectively pushed by the bulkiest propane molecules, triggering a structural transformation that enhances the propane adsorption on Zn-mes-DAT. In contrast, Zn-fum-DAT without the methyl handle exhibits a higher affinity to ethane, while the competitive propane adsorption is significantly reduced. This molecular handle engineering results in a high-purity methane yield of 9.0 mmol/cm³ on Zn-fum-DAT, representing an 80% improvement over the isoreticular material with higher propane affinity. This work provides a design blueprint for tailoring the pore chemistry in MOFs to address industrially relevant separation challenges.