Propyne/propylene (C3 H4 /C3 H6 ) separation is a critical process for the production of polymer-grade C3 H6 . However, optimization of the structure of porous materials for the highly efficient removal of C3 H4 from C3 H6 remains challenging due to their similar structures and ultralow C3 H4 concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF62- = SIFSIX, NbOF52- = NbOFFIVE) can serve as highly selective C3 H4 traps for the removal of trace C3 H4 from C3 H6 . 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 C3 H4 molecule. The pyrazine-based single-molecule trap enables extremely high C3 H4 uptake under ultralow concentration (2.65 mmol g-1 at 3000 ppm, one C3 H4 per unit cell) and record selectivity over C3 H6 at 298 K (>250). The single-molecule binding mode for C3 H4 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 C3 H4 (1000 ppm on SIFSIX-3-Ni, and 10 000 ppm on SIFSIX-2-Cu-i) from C3 H6 .