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

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.