Dinuclear Copper Sulfate-Based Square Lattice Topology Network with High Alkyne Selectivity

Porous coordination networks (PCNs) sustained by inorganic anions that serve as linker ligands can offer high selectivity toward specific gases or vapors in gas mixtures. Such inorganic anions are best exemplified by electron-rich fluorinated anions, e.g., SiF₆^2-, TiF₆^2-, and NbOF₅^2-, although sulfate anions have recently been highlighted as inexpensive and earth-friendly alternatives. Herein, we report the use of a rare copper sulfate dimer molecular building block to generate two square lattice, sql, coordination networks which can be prepared via solvent layering or slurrying, CuSO₄(1,4-bib)_1.5, 1, (1,4-bib = 1,4-bisimidazole benzene) and CuSO₄(1,4-bin)_1.5, 2, (1,4-bin = 1,4-bisimidazole naphthalene). Variable-temperature SCXRD and PXRD experiments revealed that both sql networks underwent reversible structural transformations due to linker rotations or internetwork displacements. Gas sorption studies conducted upon the narrow-pore phase of CuSO₄(1,4-bin)_1.5, 2np, found a high calculated 1:99 selectivity for C₂H₂ over C₂H₄ (33.01) and CO₂ (15.18), as well as strong breakthrough performance. Across-the-board, C₃H₄ selectivity vs C₃H₆, CO₂, and C₃H₈ was also observed. Sulfate-based PCNs, although still understudied, appear increasingly likely to offer utility in gas and vapor separations.