Systematic and exploratory access to new Ce(IV)- and mixed-Metal Ce/Zr-MOFs

• Applicant: Professor Dr. Norbert Stock
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 508229808

Metal-organic frameworks (MOFs) contain inorganic and organic building units that assemble to form 2D or 3D networks. The modular structures allow tuning the pore size and pore functionality in these materials. MOFs containing tri- and tetravalent metal ions and especially Zr-MOFs have been in the focus of many studies due to their thermal and chemical stability. The structural chemistry of Zr-MOFs is mainly characterized by the presence of hexanuclear Zr-O-clusters that are connected through organic molecules, usually carboxylate ions, to build up frameworks of various topologies. The structural chemistry of Zr-MOFs has been extended during the last few years and our group was able to discover new inorganic building units. In addition, we have developed a readily applicable synthesis route to Ce(IV)- and Ce(IV)/Zr-MOFs, which led to more than 25 new MOFs. The inorganic building unit in these crystal structures are exclusively the hexanuclear Ce(IV) and Ce(IV)/Zr-O-cluster respectively. Only lately, in 2020, Ce(IV)-MOFs containing a new inorganic building unit was reported when solvothermal reaction conditions were employed.The proposed project aims at the advancement of the synthetic and structural chemistry of Ce(IV)- and Ce(IV)/Zr-MOFs. We target the synthesis of MOFs with new inorganic building units, which will lead to the formation of new framework structures, as well as the formation of known framework structures containing inorganic building units with new Ce(IV)/Zr-compositions.To achieve these objectives two synthesis approaches will be followed. Route 1 is a more exploratory approach that relies on the use of high-throughput methods that allow the concurrent synthesis of 24 or 48 products in parallel. The solvents water and acetonitrile as well as di-, tri- and tetracarboxylic acids of different molecular geometry and flexibility will be employed. New MOFs with up to now unknown inorganic building units should be accessible through variation of the reaction parameters, such as molar ratios of stating materials, reaction temperature, overall concentration or the use of a modulator. Route 2 focuses on the synthesis and characterization of new hexanuclear Ce(IV)-O- and Ce(IV)/Zr-O-cluster. In addition to structural aspects, the local distribution of the Ce and Zr ions as well as the redox properties of the clusters will be studied. The cluster composition is expected to have a strong influence of the redox properties, which could be tuned for catalytic applications. The Ce-O- and Ce/Zr-O-clusters will be used as molecular precursors in ligand exchange reactions leading to the formation of MOFs. Mild reaction conditions will be investigated that will also allow us to study the crystallisation process by in-situ powder X-ray diffraction. Redox properties for selected Ce-O and Ce/Zr-O MOFs will also be determined. Thus, photocatalytic studies on the decomposition of dyes will be carried out.

• DFG Programme: Research Grants
• International Connection: Italy
• Cooperation Partner: Professor Dr. Ferdinando Costantino