Meltable, Glass-Forming, Iron Zeolitic Imidazolate Frameworks

Area of Science:

• Materials Science
• Chemistry
• Solid-State Chemistry

Background:

• Zeolitic imidazolate frameworks (ZIFs) are a subclass of metal-organic frameworks (MOFs) with diverse applications.
• Developing meltable MOFs and MOF glasses is an emerging area of materials research.
• Iron-based ZIFs are of particular interest due to iron's abundance and tunable properties.

Purpose of the Study:

• To synthesize and characterize the first meltable iron-based zeolitic imidazolate framework (ZIF).
• To investigate the thermal behavior, phase transformations, and glass-forming ability of the synthesized material.
• To explore the structural and mechanical properties of the resulting metal-organic framework glass.

Main Methods:

• Thermal treatment of a precursor compound ([Fe3(im)6(Him)2]) to obtain Fe(im)2.
• Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to study thermal properties.
• X-ray total scattering and nanoindentation to characterize the crystalline and glassy states.

Main Results:

• Successful synthesis of MUV-24, an iron-based ZIF, through thermal decomposition.
• Observation of crystalline phase transformations and melting at 482 °C.
• Formation of the first iron-metal-organic framework glass upon cooling, retaining tetrahedral coordination and showing increased Young's modulus.

Conclusions:

• MUV-24 represents a breakthrough as the first meltable iron-based ZIF.
• The material exhibits unique thermal behavior, transitioning from crystalline solid to liquid and then to a stable glass.
• The resulting MOF glass demonstrates enhanced mechanical properties, opening avenues for new material applications.