A Single‐Molecule Propyne Trap: Highly Efficient Removal of Propyne from Propylene with Anion‐Pillared Ultramicroporous Materials

Propyne/propylene (C₃H₄/C₃H₆) separation is a critical process for the production of polymer‐grade C₃H₆. However, optimization of the structure of porous materials for the highly efficient removal of C₃H₄ from C₃H₆ remains challenging due to their similar structures and ultralow C₃H₄ concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF₆^2? = SIFSIX, NbOF₅^2? = NbOFFIVE) can serve as highly selective C₃H₄ traps for the removal of trace C₃H₄ from C₃H₆. Especially, it is revealed that the pyrazine‐based ultramicroporous material with square grid structure for which the pore shape and functional site disposition can be varied in 0.1–0.5 Å scale to match both the shape and interacting sites of guest molecule is an interesting single‐molecule trap for C₃H₄ molecule. The pyrazine‐based single‐molecule trap enables extremely high C₃H₄ uptake under ultralow concentration (2.65 mmol g^?1 at 3000 ppm, one C₃H₄ per unit cell) and record selectivity over C₃H₆ at 298 K (>250). The single‐molecule binding mode for C₃H₄ within ultramicroporous material is validated by X‐ray diffraction experiments and modeling studies. The breakthrough experiments confirm that anion‐pillared ultramicroporous materials set new benchmarks for the removal of ultralow concentration C₃H₄ (1000 ppm on SIFSIX‐3‐Ni, and 10 000 ppm on SIFSIX‐2‐Cu‐i) from C₃H₆.