Cross-Linking CdSO₄-Type Nets with Hexafluorosilicate Anions to Form an Ultramicroporous Material for Efficient C₂H₂/CO₂ and C₂H₂/C₂H₄ Separation

A 4⁴.6¹⁰.8 topology hybrid ultramicroporous material (HUM), {[Cu_1.5F(SiF₆)(L)_2.5]·G}_n, (L = 4,4′-bisimidazolylbiphenyl, G = guest molecules), 1, formed by cross-linking interpenetrated 3D four-connected CdSO₄-type nets with hexafluorosilicate anions is synthesized and evaluated in the context of gas sorption and separation herein. 1 is the first HUM functionalized with two different types of fluorinated sites (SiF₆²⁻ and F⁻ anions) lining along the pore surface. The optimal pore size (≈5 Å) combining mixed and high-density electronegative fluorinated sites enable 1 to preferentially adsorb C₂H₂ over CO₂ and C₂H₄ by hydrogen bonding interactions with a high C₂H₂ isosteric heat of adsorption (Q_st) of ≈42.3 kJ mol⁻¹ at zero loading. The pronounced discriminatory sorption behaviors lead to excellent separation performance for C₂H₂/CO₂ and C₂H₂/C₂H₄ that surpasses many well-known sorbents. Dynamic breakthrough experiments are conducted to confirm the practical separation capability of 1, which reveal an impressive separation factor of 6.1 for equimolar C₂H₂/CO₂ mixture. Furthermore, molecular simulation and density functional theory (DFT) calculations validate the strong binding of C₂H₂ stems from the chelating fix of C₂H₂ between SiF₆²⁻ anion and coordinated F⁻ anion.