Synthesis and Structure Evolution in Metal Carbazole Diphosphonates Followed by Electron Diffraction

Area of Science:

• Materials Chemistry
• Crystallography
• Porous Materials

Background:

• Developing novel porous materials is crucial for applications in gas storage, separation, and catalysis.
• Metal phosphonates offer tunable structures and properties, but accessing diverse frameworks remains challenging.

Purpose of the Study:

• To design and synthesize new porous metal phosphonates using a novel V-shaped diphosphonic acid linker.
• To investigate the structural properties and guest sorption behavior of the resulting materials.

Main Methods:

• High-throughput screening of metal salts with 3,6-diphosphono-9H-carbazole (H4L).
• Structure determination using electron diffraction.
• In situ dehydration studies and water sorption measurements.
• Powder X-ray diffraction for structural analysis.

Main Results:

• Two porous metal phosphonates, CAU-37 and CAU-57, were successfully synthesized.
• CAU-37 displays intralayer water de-/adsorption, causing an 11.9% cell volume change and "accordion-like" flexibility.
• CAU-57 features a layered inorganic building unit (IBU) leading to pore formation due to the rigid linker.
• Reversible water sorption with structural retention was confirmed for both materials.

Conclusions:

• The V-shaped diphosphonic acid linker is effective in creating porous metal phosphonates with unique structural features.
• CAU-37 demonstrates significant structural flexibility and dynamic behavior upon water adsorption/desorption.
• The study highlights the potential of rationally designed linkers for accessing novel porous frameworks.