Engineering Metal–Organic Frameworks for Selective Separation of Hexane Isomers Using 3‑Dimensional Linkers

Metal–organic frameworks (MOFs) are highly tunable materials with potential for use as porous media in non-thermal adsorption or membrane-based separations. However, many separations target molecules with sub-angstrom differences in size, requiring precise control over the pore size. Herein, we demonstrate that this precise control can be achieved by installing a three-dimensional linker in an MOF with one-dimensional channels. Specifically, we synthesized single crystals and bulk powder of NU-2002, an isostructural framework to MIL-53 with bicyclo[1.1.1]­pentane-1,3-dicarboxylic acid as the organic linker component. Using variable-temperature X-ray diffraction studies, we show that increasing linker dimensionality limits structural breathing relative to MIL-53. Furthermore, single-component adsorption isotherms demonstrate the efficacy of this material for separating hexane isomers based on the different sizes and shapes of these isomers.