Dinuclear Nickel-Oxygen Cluster-Based Metal-Organic Frameworks with Octahedral Cages for Efficient Xe/Kr Separation

Xe/Kr separation is industrially important but remains a daunting issue in chemical separations. Herein, a fluorinated metal-organic framework (MOF), [Ni₂(μ₂-O)(TFBPDC)(tpt)₂] (named JXNU-13-F), built from 3,3',5,5'-tetrakis(fluoro)biphenyl-4,4'-dicarboxylic (TFBPDC^2-) and 2,4,6-tri(4-pyridinyl)-1,3,5-triazine (tpt) ligands is provided. JXNU-13-F displays a three-dimensional (3D) framework constructed from distorted octahedral cages and an impressive Xe capacity of 144 cm³ g^-1 at 273 K and 1 bar, ranking among top MOFs. The high Xe uptake and moderate Xe/Kr adsorption selectivity endow JXNU-13-F with efficient Xe/Kr separation demonstrated by experimental column breakthrough tests. The comparative studies of gas adsorption between isostructural JXNU-13-F and JXNU-13 (the nonfluorinated analogue ([Ni₂(μ₂-O)(BPDC))(tpt)₂] with biphenyl-4,4'-dicarboxylic (BPDC^2-)) revealed that the F groups serve as the innocent groups during the Xe and Kr adsorption in JXNU-13-F. Thus, a combination of highly hydrophobic and π-electron-rich pore surfaces made of aromatic rings with strong interactions with the Xe atom possessing large polarizability and appropriate pore sizes that match well Xe having a large atom diameter has resulted in high Xe uptake and effective Xe/Kr separation characteristics of JXNU-13-F.