New Isostructural Family of Mixed-Metal Na-M(III)-MOFs Based on Glycolic Acid

A series of new isostructural metal–organic frameworks based on trivalent metal ions (Al, Fe, Ga), Na+ ions and glycolate ions as the linker molecules, denoted as M-CAU-64, with the framework composition [M(III)Na(H2O)2(C2H2O3)2] · x H2O were obtained using high-throughput methods. The crystal structures of the title compounds were determined from single crystal or powder X-ray diffraction data. Thermogravimetric analyses indicate a thermal stability up to 340 °C for Ga-CAU-64, while variable temperature powder X-ray diffraction (VT-PXRD) revealed various structural changes including phase transformations and a rearrangement of the inorganic building unit of CAU-64, associated with the loss of adsorbed water molecules upon thermal treatment. Water sorption measurements confirmed the porosity of the CAU-64 compounds and sorption capacities up to 360 mg/g were found. Furthermore, the synthesis of multivariate MOFs (Alx-Fe1-x-CAU-64) enabled the fine-tuning of both thermal stability and sorption characteristics.