Construction of a Polyhedral Metal–Organic Framework via a Flexible Octacarboxylate Ligand for Gas Adsorption and Separation

A flexible octacarboxylate ligand, tetrakis­[(3,5-dicarboxyphenyl)­oxamethyl]­methane (H₈X), has been used to construct a highly porous metal–organic framework (In₂X)­(Me₂NH₂)₂(DMF)₉(H₂O)₅ (1), which is comprised of octahedral and cuboctahedral cages and shows a rare (4,8)-connected scu topology. Gas adsorption studies of N₂, H₂ on the actived 1 at 77 K reveal a Langmuir surface area of 1707 m² g^–1, a BET surface area of 1555 m² g^–1, a total pore volume of 0.62 cm³ g^–1, and a H₂ uptake of 1.49 wt % at 1 bar and 3.05 wt % at 16 bar. CO₂, CH₄, and N₂ adsorption studies at 195, 273, 285, and 298 K and also ideal adsorbed solution theory (IAST) calculations demonstrate that 1 has high selectivites of CO₂ over CH₄ and N₂. The resulting framework represents a MOF with the highest gas uptakes and gas selectivities (CO₂ over CH₄ and N₂) constructed by flexible ligands.