Creating Order in Ultrastable Phosphonate Metal-Organic Frameworks via Isolable Hydrogen-Bonded Intermediates

Area of Science:

• Materials Science
• Inorganic Chemistry
• Crystallography

Background:

• Trivalent metal-organic frameworks (MOFs) offer promising stability.
• Crystallizing phosphonate-based MOFs is challenging due to complex binding motifs and irreversible self-assembly.
• Hydrogen-bonded MOFs (HMOFs) can serve as crystalline intermediates for MOF synthesis.

Purpose of the Study:

• To synthesize a new porous HMOF using phosphonate ligands and a Cr(III) source.
• To convert the synthesized HMOF into an ordered Cr(III)-phosphonate MOF via dehydration.
• To evaluate the stability and structural properties of the resulting MOF.

Main Methods:

• Synthesis and crystallographic characterization of a new HMOF (H-CALF-50).
• Dehydration of H-CALF-50 to form the target MOF (CALF-50).
• Assessment of CALF-50's stability under harsh conditions (boiling water, concentrated acids) and characterization of its structure using computational methods.

Main Results:

• A new porous HMOF, H-CALF-50, was successfully synthesized and characterized.
• Dehydration of H-CALF-50 yielded the ordered, albeit not single-crystalline, MOF CALF-50.
• CALF-50 demonstrated exceptional stability, retaining crystallinity and surface area after prolonged exposure to boiling water and concentrated acids.

Conclusions:

• The dehydration of HMOFs provides a viable route to synthesize stable Cr(III)-phosphonate MOFs.
• CALF-50 exhibits remarkable chemical and thermal robustness, indicating its potential for applications requiring high stability.
• Computational studies offered insights into the structural transformation and heterogeneity during the HMOF to MOF conversion.