Metal–organic frameworks containing coordinatively unsaturated metal sites offer advantages in catalysis and gas capture due to electronic host-guest interaction with the metal site. By altering the metal, one can tune the chemical and physical properties of the material. MAF-X27, a series of azolate MOFs with 1D hexagonal channels and open metal sites, has been studied for gas uptake and storage with Cu, Co, Ni, Mg, and Fe analogues. However, the material has not yet been accessed with Zn(II) comprising the node since the de novo reaction of Zn(II) and the linker, 1H,5H-benzo(1,2-d:4,5-d’)bistriazole (H2BBTA), results in the cubic pcu MOF with Zn5 nodes, MFU-4, rather than the desired etb topology. Herein, we utilized a post-synthetic technique, namely solvent-assisted linker exchange (SALE), with Zn-MOF-74—a MOF that is isostructural with MAF-X27 and has been extensively studied for gas uptake—to exchange its 2,5-dioxidoterephthalate (dobdc) linker for H2BBTA. The resulting MOF, NU-250, contains a coordination sphere comprised of Zn–N bonds as opposed to Zn–O thus tuning the identity and electronics of the framework at the metal nodes. NU-250 was further characterized and tested for CO2 uptake, showing about 5 kJ/mol increase in isosteric heat of adsorption compared to the parent Zn-MOF-74. While SALE is known to be a viable route to access MOFs that are challenging to synthesize de novo, this is, to the best of our knowledge, the first study to show a successful linker exchange that incorporates a new coordinating functional group to the node.

Exchange of coordinated carboxylates with azolates as a route to obtain a microporous zinc–azolate framework

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