UoC‐2: A Fluorinated Derivative of the Robust Metal‐Organic Framework MFM‐300

By solvothermal reactions of fluoro substituted biphenyl‐3,3’,5,5’‐tetracarboxylic acids (H4BPTC) with the respective metal salts, four new MOFs with the MFM‐300 topology were synthesized, namely [MIII2(OH)2(L)] with MIII=Ga3+, In3+ and L=4‐mF‐BPTC4− and 4,4’‐dF‐BPTC4−. Three of them were refined from X‐ray single crystal diffraction data (I4122, Z=4), [Ga2(OH)2(4,4’‐dF‐BPTC)] was confirmed by Le Bail fits based on synchrotron powder diffraction data. To the best of our knowledge, these four compounds represent the very first examples of MFM‐300 type MOFs with a substituted BPTC4− linker. With increasing fluorination of the linker, the thermal stability decreases, as the decarboxylation of the linker is facilitated. On the other hand, the gas uptake is enhanced significantly. E.g. the CO2 uptake (273 K, 1 bar) increases from 124 cm3/g for [Ga2(OH)2(4‐mF‐BPTC)] to 136 cm3/g for [Ga2(OH)2(4,4’‐dF‐BPTC)]. Surprisingly, the exact determination of specific surface areas (SBET) turned out to be difficult. It is supposed that due to transient open metal sites, complete removal of solvent molecules (DMF, acetone) is not always possible before degradation of the framework starts. By incorporating mono‐ or difluorinated BPTC (biphenyl‐3,3’,5,5’‐tetracarboxylate) linkers, the first fluorinated MOFs with MFM‐300 topology are obtained. They contain Ga3+ or In3+ nodes and are named UoC‐2 (University of Cologne). As the number of fluorine substituents increases, a significant increase in CO2 uptake is observed, while thermal stability decreases as decarboxylation of the linker is facilitated.