Crystal Engineering of a New Hexafluorogermanate Pillared Hybrid Ultramicroporous Material Delivers Enhanced Acetylene Selectivity

Hybrid ultramicroporous materials (HUMs), metal-organic platforms that incorporate inorganic pillars, are a promising class of porous solids. A key area of interest for such materials is gas separation, where HUMs have already established benchmark performances. Thanks to their ready compositional modularity, we report the design and synthesis of a new HUM, GEFSIX-21-Cu, incorporating the ligand pypz (4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, 21) and GeF₆^2- pillaring anions. GEFSIX-21-Cu delivers on two fronts: first, it displays an exceptionally high C₂H₂ adsorption capacity (≥5 mmol g^-1) which is paired with low uptake of CO₂ (<2 mmol g^-1), and, second, a low enthalpy of adsorption for C₂H₂ (ca. 32 kJ mol^-1). This combination is rarely seen in the C₂H₂ selective physisorbents reported thus far, and not observed in related isostructural HUMs featuring pypz and other pillaring anions. Dynamic column breakthrough experiments for 1:1 and 2:1 C₂H₂/CO₂ mixtures revealed GEFSIX-21-Cu to selectively separate C₂H₂ from CO₂, yielding ≥99.99% CO₂ effluent purities. Temperature-programmed desorption experiments revealed full sorbent regeneration in <35 min at 60 °C, reinforcing HUMs as potentially technologically relevant materials for strategic gas separations.