A Chemically Cross-Linked NbO-Type Metal-Organic Framework: Cage or Window Partition?

By using a presynthetically cross-linked octacarboxylate ligand, a chemically cross-linked version of the NbO-type metal-organic framework (MOF) NOTT-101 (ZJNU-80) was prepared. Single-crystal X-ray structure analysis showed that ZJNU-80 adopts the same topology as the parent compound NOTT-101, and the tethering groups take part in the window partition, not the cage partition. The gas adsorption studies showed that, despite the lower porosity, ZJNU-80a exhibits low-pressure gas adsorption behavior similar to that of the parent MOF NOTT-101a toward CO2, CH4, and N-2 at ambient temperature because of the fact that the window partition as a result of chemical cross-linking does not almost alter the pore-size distributions. However, different adsorption behaviors toward 1-butene, a molecule with even larger kinetic diameter than that of the aforementioned adsorbates, were observed because the window partition alters the efficiency with which 1-butene molecules pack within ZJNU-80a and NOTT-101a at conditions close to saturation. This work provides a fundamental understanding on the effect of chemical cross-linking on the MOF's structure and gas adsorption properties.