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.