“Click” on MOFs: A Versatile Tool for the Multimodal Derivatization of N3-Decorated Metal Organic Frameworks

Postsynthetic modification (PSM) has been exploited for the preparation of two novel N3-decorated MOFs, namely, UMCM-1-N3 [Zn4O(N3tpa)(btb)4/3;N3tpa2−=2-azidoterephthalate; btb3−= 4,4′,4″-benzene-1,3,5-triyl-tribenzoate] and MIXMOF-5-N3 [Zn4O(N3tpa)0.4(tpa)2.6; tpa2−= terephthalate], featured by both different azido functional group content and crystalline structure. Subse-quently, the as-synthesized materials were further transformed through an efficient and versatile approach capable of imparting multimodality to these porous organic−inorganic polymers. Cu-mediated acetylene−azide coupling (CuAAC; “click”reaction) has been performed in a single step, under optimized conditions, with complete azido →triazole conversion using either single acetylene derivatives or mixtures of reactive terminal alkynes in variable molar fractions to give homo- and heteroderivatized MOFs. An accurate control of the relative percentages of the functional groups in thefinal heterofunctionalized materials is conveniently achieved through afine-tuning of the starting acetylene mixtures molar ratio. All MOFs derivatives have been characterized through thermogravimetric analysis coupled with MS analysis of volatiles (TG-MS), powder X-ray diffraction (PXRD), FT-IR spectroscopy, and 1H NMR spectroscopy of the digested functionalized samples. Fluorescence studies on properly labeled (dye-functionalized) MOFs have been used for thefirst time to assess the statistical distribution of the“reactive probe”throughout the bulk material.