Anhydride Post-Synthetic Modification in a Hierarchical Metal–Organic Framework

Abstract

Metal-organic frameworks (MOFs) are important porous materials. Post-synthetic modification (PSM) of MOFs via the pendant groups or secondary functional groups of organic linkers has been widely used to introduce new, or enhance existing properties of MOFs for various practical applications. In this work, we have constructed, for the first time, a novel platform for PSM of MOFs by introducing anhydride functional group into a hierarchically porous MOF (MIL-121) as an effective anchor. We have demonstrated that a combination of high reactivity of anhydride and hierarchical porosity makes this protocol particular novel and important as it led to excellent opportunities of incorporating not only a wide variety of organic molecules with different sizes and chemical nature, but also the noble metal complexes in MOFs. Specifically, we show that the anhydride group decorated in the MOF exhibits a high reactivity towards covalently binding 10 different guest molecules including alcohols, amines, thiols and noble metal (Pt(II)/Pt(IV)) complexes, whereas the hierarchical pores created in the MOF allow the incorporation of guest species varying in size from methanol to larger molecules such as polyaromatic amines. This novel approach provides the community with a new avenue to prepare MOF-based materials for targeted applications. To illustrate this point, we furnish an example of using this new platform to prepare a Pt-based electrocatalyst which shows excellent catalytic activity towards the oxygen reduction reaction (ORR), a pivotal half-reaction in hydrogen-oxygen fuel cells and other energy storage devices.