Two Anhydrous Salts of Tetrafluoroterephthalic Acid (H2tF-BDC): K2tF-BDC and Rb2tF-BDC

Two new anhydrous salts of tetrafluoroterephthalic acid (H(2)tF-BDC), namely K(2)tF-BDC (1) and Rb(2)tF-BDC (2), were synthesized and structurally characterized. The crystal structure of 1 (I2/m, Z = 2) was solved and refined from X-ray single crystal data. K+ (CN = 8) is coordinated by six oxygen atoms of five different tF-BDC2- linkers and two fluorine atoms of two of these linkers, which connect the KO6F2 polyhedra to a 3D network. The crystal structure of 2 (P, Z = 1) was refined from X-ray powder diffraction data. It crystallizes in a structure type already known from Tl(2)tF-BDC. Rb+ (CN = 8) is also coordinated by six oxygen and two fluorine atoms. But six tF-BDC2- linkers are involved in the coordination. Again, a 3D network is formed. Both compounds can be obtained as single-phase samples. They are not porous and stable in air. The thermal stability was investigated by DTA/TG measurements. The decomposition starts at approx. 200 degrees C (1) and 230 degrees C (2). Their good solubility in water makes them interesting starting materials for the synthesis of new MOFs with the perfluorinated linker tF-BDC2-.