Side-Arm Sterics Direct Conformation, Topology, and Function in Zirconium Metal–Organic Frameworks

Abstract

While steric control of linker conformation has proven effective for accessing new Zr-MOF structures, existing strategies have largely relied on modification of the linker core—an approach that intrinsically couples steric effects to framework connectivity, limits available functionalization sites, and often requires complex synthesis, particularly for high-connectivity linkers. Here, we introduce a conceptually distinct and adaptable strategy for topological control based on steric modulation through side-arm functionalization, which enables independent steric tuning without altering linker connectivity while remaining synthetically simple. Six amide or cyano groups positioned on the ligand side arms act as unconventional steric units to induce isolable conformational variability. This design enables the linker to flex and twist, guiding the formation of two isostructural Zr-MOFs, AM-Zr-1 and CN-Zr-1, adopting the rare underlying net 6,8-c nuh1 (or 3,8-c nuh2) with highly distorted, topologically complex porous architectures. Despite their identical connectivity, AM-Zr-1 generates a geometrically unique amide pocket that enhances CO2 binding and affords higher CO2/N2 and CO2/CH4 selectivity, whereas the less bulky cyano substituents confer a more extended conformation to CN-Zr-1, resulting in higher surface area and H2 uptake. These findings highlight steric side-arm functionalization as a simple yet versatile strategy for tuning Zr-MOF topology and function.