Topological Design of Unprecedented Metal-Organic Frameworks Featuring Multiple Anion Functionalities and Hierarchical Porosity for Benchmark Acetylene Separation

Separation of acetylene (C₂H₂) from carbon dioxide (CO₂) or ethylene (C₂H₄) is industrially important but still challenging so far. Herein, we developed two novel robust metal organic frameworks AlFSIX-Cu-TPBDA (ZNU-8) with znv topology and SIFSIX-Cu-TPBDA (ZNU-9) with wly topology for efficient capture of C₂H₂ from CO₂ and C₂H₄. Both ZNU-8 and ZNU-9 feature multiple anion functionalities and hierarchical porosity. Notably, ZNU-9 with more anionic binding sites and three distinct cages displays both an extremely large C₂H₂ capacity (7.94 mmol/g) and a high C₂H₂/CO₂ (10.3) or C₂H₂/C₂H₄ (11.6) selectivity. The calculated capacity of C₂H₂ per anion (4.94 mol/mol at 1 bar) is the highest among all the anion pillared metal organic frameworks. Theoretical calculation indicated that the strong cooperative hydrogen bonds exist between acetylene and the pillared SiF₆²⁻ anions in the confined cavity, which is further confirmed by in situ IR spectra. The practical separation performance was explicitly demonstrated by dynamic breakthrough experiments with equimolar C₂H₂/CO₂ mixtures and 1/99 C₂H₂/C₂H₄ mixtures under various conditions with excellent recyclability and benchmark productivity of pure C₂H₂ (5.13 mmol/g) or C₂H₄ (48.57 mmol/g).