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

Propyne/propylene (C 3 H 4 /C 3 H 6 ) separation is a critical process for the production of polymer‐grade C 3 H 6 . However, optimization of the structure of porous materials for the highly efficient removal of C 3 H 4 from C 3 H 6 remains challenging due to their similar structures and ultralow C 3 H 4 concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF 6 2− = SIFSIX, NbOF 5 2− = NbOFFIVE) can serve as highly selective C 3 H 4 traps for the removal of trace C 3 H 4 from C 3 H 6 . 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 C 3 H 4 molecule. The pyrazine‐based single‐molecule trap enables extremely high C 3 H 4 uptake under ultralow concentration (2.65 mmol g −1 at 3000 ppm, one C 3 H 4 per unit cell) and record selectivity over C 3 H 6 at 298 K (>250). The single‐molecule binding mode for C 3 H 4 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 C 3 H 4 (1000 ppm on SIFSIX‐3‐Ni, and 10 000 ppm on SIFSIX‐2‐Cu‐i) from C 3 H 6 .