Metal-organic frameworks (MOFs) share some common features with enzymes including reactive site isolation, well-defined secondary structures, and the ability to support entatic states poised for reaction with a substrate. However, unlike many metalloenzymes, MOFs are often limited to the reactivity available at isolated metal sites. This presentation will highlight our recent efforts to design MOFs with cooperative reactivity for CO2 capture and nitric oxide reduction. Postsynthetic modifications have been used to generate M–OH (M = Co, Ni, Zn) groups at the inorganic building units of the benzotriazolate-based MOFs CFA-1, MFU-4, and MFU-4l. The resulting materials adsorb large amounts of CO2 via a chemisorption process reminiscent of CO2 fixation by α-carbonic anhydrases. A biomimetic Fe2+ pyrazolate MOF featuring unusual chain-type metal nodes with accessible coordination sites on adjacent metal centers will also be discussed. The diiron motifs in this material resemble the active sites of non-heme diiron enzymes, such as flavodiiron nitric oxide reductases (FNORs), that use cooperative substrate activation to carry out multielectron redox processes. Remarkably, the Fe2+ MOF generates N2O in nearly quantitative yield upon exposure to stoichiometric amounts of NO, emulating the reactivity of FNORs and representing a rare example of direct NO reduction from a diferrous model complex.

Biomimetic reactivity in MOFs for gas separation and catalysis

ACS Spring 2022

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