How Does the Fluorination of the Linker Affect the Stability of Trimesate-Based Coordination Polymers and Metal–Organic Frameworks?

Abstract

The syntheses and crystal structures of the monopotassium salts of difluorinated and tri/perfluorinated trimesic acid (1,3,5-benzenetricarboxylic acid ≡ H3BTC) are presented, namely, K(H2 dF-BTC) ( Fdd2, Z = 16) and K(H2 pF-BTC) ( Cc, Z = 4). For the first time, together with already known K(H2 mF-BTC), all fluorination degrees of trimesic acid are accessible and can be used for a systematic study of the influence of fluorination on the stability of the resulting coordination polymers and metal-organic frameworks (MOFs). The monopotassium salts show a decreasing (chemical) stability in water upon heating, as well as a decreasing thermal stability, as evidenced by differential scanning calorimetry/thermogravimetric analysis (DSC/TGA). A similar decreasing thermal stability is found for two series of isostructural coordination polymers (UHM-33 topology: ∞2[Cu2(L)2(DMA)2]·2DMA with L2- = H mF-BTC2- and H dF-BTC2-) and MOFs (∞3[Ba(L)(H2O)2]·1/2H2O with L2- = HBTC2-, H mF-BTC2- and H dF-BTC2-). Remarkably, while the decomposition temperatures decrease with increasing fluorination of the linker, the releasing temperatures for embedded solvent molecules (DMA and H2O, respectively) increase. To identify possible candidates for the synthesis of isostructural coordination polymers and MOFs with BTC3- ligands with different degrees of fluorination, a database-adapted approach was developed, which utilizes the increased torsion angle between the carboxylate groups and the phenyl rings in these materials as a structure-determining parameter.