RESUMEN
A new Zr-based metal-organic framework denoted as Zr-CAU-28 with framework composition [Zr6O4(OH)4(FDC)4(OH)4(H2O)4] (H2FDC = 2,5-furandicarboxylic acid, CAU = Christian-Albrechts-University) was obtained under green synthesis conditions from a mixture of H2O and acetic acid and employing microwave-assisted heating. Zr-CAU-28 is the first Zr-MOF based on H2FDC, which is often considered a promising renewable alternative to terephthalic acid. The crystal structure was determined from powder X-ray diffraction data using a combination of direct methods, force field calculations, and Rietveld refinement. The compound crystallizes in the hexagonal crystal system (space group P63/mmc) with the cell parameters a = 24.9919(9) and c = 24.7688(9) Å. The framework structure adopts a kagome-like topology and hence contains large hexagonal channels with a pore diameter of approximately 16 Å and small trigonal channels with a size of 3 Å. Nitrogen sorption measurements were carried out at -196 °C and gave a specific surface area of SBET = 1006 m2/g and a micropore volume of 0.42 cm3/g. Thermogravimetric analyses showed a stability up to 270 °C although temperature dependent PXRD measurements revealed a decrease in long-range order already above 150 °C. Furthermore, the Ce4+ based analogue Ce-CAU-28 could be obtained employing dimethylformamide/water mixtures as solvent. The structure and framework composition of this MOF are very similar to the ones of the Zr-based compound, but its thermal stability is clearly inferior. Thus, Ce-CAU-28 cannot be fully desolvated and exhibits a specific surface area of only SBET = 360 m2/g and a micropore volume of 0.15 cm3/g.
RESUMEN
New single- and mixed-linker Cr-MIL-101 derivatives bearing different functional groups have been synthesized. The influence of the reaction parameters, such as metal source (CrO3, CrCl3, and Cr(NO3)3·9H2O) or linker composition, on product formation have been investigated using high-throughput methods. Highly crystalline Cr-MIL-101 materials were obtained with CrCl3 as the metal source with either 2-bromoterephthalic (TA-Br) or 2-nitroterephthalic (TA-NO2) acid as one of the mixed-linker components. On the basis of these results, numerous new mixed-linker Cr-MIL-101 derivatives containing -NH2, -NO2, -H, -SO3H, -Br, -OH, -CH3, and -COOH have been synthesized. The use of TA-NH2 and TA-OH were shown, under the same reaction conditions, to lead to decarboxylation and the formation of 3-amino- and 3-hydroxybenzoic acid, respectively. Furthermore, we were also able to directly synthesize single-linker Cr-MIL-101-X derivatives with X = F, Cl, Br, CH3. Postsynthetic modification was used to selectively reduce the mixed-linker compound Cr-MIL-101-Br-NO2 to Cr-MIL-101-Br-NH2. To establish the successful incorporation of the linker molecules and possible decomposition of certain starting materials, (1)H NMR spectra of dissolved reaction products were recorded.
RESUMEN
A series of nine Ce(iv)-based metal organic frameworks with the UiO-66 structure containing linker molecules of different sizes and functionalities were obtained under mild synthesis conditions and short reaction times. Thermal and chemical stabilities were determined and a Ce-UiO-66-BDC/TEMPO system was successfully employed for the aerobic oxidation of benzyl alcohol.
RESUMEN
Postsynthetic modification can be used to introduce sulfonamide functionalities into MOF frameworks. Using sulfonyl chlorides as reactive intermediates, Cr-MIL-SO3H and CAU-1-NH2 have been further modified to give hitherto unknown functionalized MOFs in which a sulfonamide group is bound to the framework either by its N or its S atom.