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-1 H -pyrazol-4-yl)pyridine, 21 ) and GeF 6 2- pillaring anions. GEFSIX-21-Cu delivers on two fronts: first, it displays an exceptionally high C 2 H 2 adsorption capacity (≥5 mmol g -1 ) which is paired with low uptake of CO 2 (<2 mmol g -1 ), and, second, a low enthalpy of adsorption for C 2 H 2 ( ca . 32 kJ mol -1 ). This combination is rarely seen in the C 2 H 2 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 C 2 H 2 /CO 2 mixtures revealed GEFSIX-21-Cu to selectively separate C 2 H 2 from CO 2 , yielding ≥99.99% CO 2 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.