Solvent-Free and Time Efficient Postsynthetic Modification of Amino-Tagged Metal–Organic Frameworks with Carboxylic Acid Derivatives

Abstract

A fast, simple, and effective approach for postsynthetic modification (PSM) of amino-tagged metal–organic frameworks (MOFs) with carboxylic acids, acid anhydrides, and acid chlorides without additional solvent at elevated temperature was developed. In a comparative study optimal synthesis conditions for PSM were determined by systematic variation of the reactants in terms of reactivity and size for MIL-53(Al)-NH2, UiO-66(Zr)-NH2, and MIL-101(Al)-NH2. For this purpose, an acid-free digestion was prepared that allows accurate yield comparison of synthesized acid sensitive amides employing solution nuclear magnetic resonance (NMR). For MIL-53(Al)-NH2 and UiO-66(Zr)-NH2 best results were obtained using acid chlorides or anhydrides at 100 °C. For MIL-101(Al)-NH2 the application of acid anhydrides up to 100 °C was a suitable pathway for an efficient PSM. Optimization of all reaction parameters led to a postfunctionalization yield with acetic anhydride at 100 °C of 94.9 ± 0.5% for 2 h reaction time with MIL-53(A...