Pillar Modularity in fsc Topology Hybrid Ultramicroporous Materials Based upon Tetra(4-pyridyl)benzene

Abstract

Hybrid ultramicroporous materials (HUMs) are porous coordination networks composed of combinations of organic and inorganic linker ligands with a pore diameter of <7 Å. Despite their benchmark gas sorption selectivity for several industrially relevant gas separations and their inherent modularity, the structural and compositional diversity of HUMs remains underexplored. In this contribution, we report a family of six HUMs (SIFSIX-22-Zn, TIFSIX-6-Zn, SNFSIX-2-Zn, GEFSIX-4-Zn, ZRFSIX-3-Zn, and TAFSEVEN-1-Zn) based on Zn metal centers and the tetratopic N-donor organic ligand tetra(4-pyridyl)benzene (tepb). The incorporation of fluorinated inorganic pillars (SiF₆ ^2-, TiF₆ ^2-, SnF₆ ^2-, GeF₆ ^2-, ZrF₆ ^2-, and TaF₇ ^2-, respectively) resulted in (4,6)-connected fsc topology as verified using single-crystal X-ray diffraction. Pure-component gas sorption studies with N₂, CO₂, C₂H₂, C₂H₄, and C₂H₆ revealed that the large voids and narrow pore windows common to all six HUMs can be leveraged to afford high C₂H₂ uptakes while retaining high ideal adsorbed solution theory (IAST) selectivities for industrially relevant gas mixtures: >10 for 1:99 C₂H₂/C₂H₄ and >5 for 1:1 C₂H₂/CO₂. The approach taken, systematic variation of pillars with retention of structure, enables differences in selectivity to be attributed directly to the choice of the inorganic pillar. This study introduces fsc topology HUMs as a modular platform that is amenable to fine-tuning of structure and properties.