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

Abstract

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. Subsequently, 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 the final heterofunctionalized materials is conveniently achieved through a fine-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 the first time to assess the statistical distribution of the “reactive probe” throughout the bulk material.