Structure and Properties of Metal-Organic Frameworks under Hydrostatic Pressures

• Applicant: Dr. Gregor Kieslich
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 533641606

By combining inorganic coordination chemistry and organic linker chemistry, Metal-Organic Frameworks (MOFs) provide a virtually unlimited chemical space to target material responsiveness through chemical changes. Their main structural feature is an open network structure which often results in a large structural response to pressure as an external stimulus. High-pressure structural research on MOFs relates to properties of academic and technological relevance such as negative linear compressibility, mechanical stability, mechanical energy storage, solid-state refrigeration, and sensing amongst others. First guidelines of how a MOF’s crystal chemistry (topology, void space, metal-node coordination number, linker geometry, defect concentration) determines its response to pressure have been formulated, and their improvement will enable the knowledge-based optimization of material stabilities and mechanical properties. In parallel, MOFs as a versatile material platform allow for embracing new research directions in the future, such as the study of charge transport properties of electrically conductive MOFs as a function of pressure - an untouched research area with manifold opportunities in applied and academic research. Looking at the current state of the field, high-pressure research on MOFs has reached a tipping point: fascinating research examples have been reported, but current high-pressure powder X-ray diffraction (HPPXRD) cells are insufficient for efficiently advancing fundamental high-pressure crystal chemistry principles and starting new research directions in the future. To unfold the potential of this research area, the targeted development of experimental techniques tightly coupled to chemical synthesis is key. Here we propose the design and application of a new HPPXRD cell dedicated for soft materials such as MOFs, where established setups such as Diamond Anvil Cells have their drawbacks. The new cell will enable HPPXRD measurements up to a pressure of 1 GPa with a pressure step-size of 0.015 GPa, easy sample loading procedures to guarantee a high-sample throughput and will enable to measure electrical conductivity alongside HPPXRD measurements, overall advancing high-pressure research capabilities for MOFs and soft materials. Armed with this setup, we propose to clarify and improve existing structure-property relations that determine the mechanical properties such as bulk modulus and cycling stability of (flexible) MOFs and provide proof-of-principle studies related to the high-pressure dependency of charge transport properties in electrically conductive MOFs. We expect that the new HPPXRD cell will become a cornerstone for high-pressure research on MOFs, and more generally soft crystalline materials, and that the research outcomes will help to approach the long-term vision of this research area: the formation of a chemical intuition for the high-pressure behavior of soft, functional materials.

• DFG Programme: Research Grants
• Major Instrumentation: Hydraulisch, Elektrische getriebene Pumpen
• Instrumentation Group: 8020 Pumpen für Flüssigkeiten