Uncoordinated Hexafluorosilicates in a Microporous Metal–Organic Framework Enabled C₂H₂/CO₂ Separation

Abstract

Metal–organic frameworks (MOFs) represent a kind of low-energy physisorbent with modifiable pores and framework structures; however, a deep understanding of how these structural features influence properties is a prerequisite for the rational design and development of tailor-made materials for advanced applications. In this report, a MOF, [Ni2(TCPP-Ni)1/4(TPIM)2(COOH)­F]­[(Me2NH2)­SiF6]·xS (SDU-CP-1; S = solvent molecules, SDU = Shandong University, and CP = coordination polymer), assembled by tetrakis­(4-carboxyphenyl)­porphyrin (TCPP-Ni) and 2,4,5-tris­(4-pyridyl)­imidazole (TPIM) ligands as well as Ni2+ cations is reported. Interestingly, inorganic SiF62– anions do not serve as the pillars like precedents in the framework but are just counterions, which endows SDU-CP-1 with high uptake for C2H2 and adsorption selectivity (2.5–4.2) for C2H2/CO2 at room temperature, as certified by gas adsorption and separation experiments and grand canonical Monte Carlo calculation