The First Sulfate-Pillared Hybrid Ultramicroporous Material, SOFOUR-1-Zn, and Its Acetylene Capture Properties

Hybrid ultramicroporous materials, HUMs, are comprised of metal cations linked by combinations of inorganic and organic ligands. Their modular nature makes them amenable to crystal engineering studies, which have thus far afforded four HUM platforms (as classified by the inorganic linkers). HUMs are of practical interest because of their benchmark gas separation performance for several industrial gas mixtures. We report herein design and gram-scale synthesis of the prototypal sulfate-linked HUM, the fsc topology coordination network ([Zn(tepb)(SO₄)]_n), SOFOUR-1-Zn, tepb=(tetra(4-pyridyl)benzene). Alignment of the sulfate anions enables strong binding to C₂H₂ via O⋅⋅⋅HC interactions but weak CO₂ binding, affording a new benchmark for the difference between C₂H₂ and CO₂ heats of sorption at low loading (ΔQ_st=24 kJ mol⁻¹). Dynamic column breakthrough studies afforded fuel-grade C₂H₂ from trace (1 : 99) or 1 : 1 C₂H₂/CO₂ mixtures, outperforming its SiF₆²⁻ analogue, SIFSIX-22-Zn.