Building ultramicroporous zirconium metal‒organic frameworks with ligands of high coordination density through a reticular approach

The rational design and synthesis of ultramicroporous solids featuring uniform pore dimensions remains a notable challenge, yet these materials are critical for the selective discrimination of molecules with similar physicochemical properties. Here we report a family of ten ultramicroporous zirconium-based metal–organic frameworks assembled from isophthalate-based octatopic or hexatopic carboxylate linkers with high coordination density and Zr₆ nodes with relatively low connectivity (4, 6 and 8). The diverse inorganic node geometry, ligand connectivity, structural topology, framework stability and ultramicroporosity of the resultant metal–organic frameworks underscore the pivotal role of linker geometry and functionality in tailoring the adsorptive properties of the material. These ultramicroporous solids hold promise for the separation of industrially relevant hydrocarbons. We show that HIAM-802 and HIAM-601 exhibit high-efficiency separation of hexane isomers based on branching by molecular exclusion. We validated their separation capabilities through breakthrough experiments and further clarified the underlying adsorption mechanisms by density functional theory calculations.