Halogenated Metal-Organic Framework Glasses and Liquids

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.
• Mixed-ligand approaches offer tunable properties in MOF synthesis.
• Understanding the relationship between structure and properties in ZIFs is crucial for materials design.

Purpose of the Study:

• To synthesize novel crystalline ZIF structures using a mixed-ligand approach.
• To investigate the glass-forming behavior and melting properties of these novel ZIFs.
• To explore the impact of halogenated ligands on ZIF properties, particularly gas uptake.

Main Methods:

• Synthesis of four novel crystalline ZIF structures via a mixed-ligand approach.
• Characterization using solid-state Nuclear Magnetic Resonance (NMR) spectroscopy.
• Spectroscopic analysis using terahertz (THz) and far-infrared (far-IR) techniques, including in situ measurements.
• Evaluation of gas-uptake properties.

Main Results:

• Successful synthesis of four novel ZIF structures exhibiting glass-forming behavior.
• Melting temperatures are influenced by electronic and steric effects of the ligands.
• Evidence of Zn-F bonds in fluorinated ZIF glasses confirmed by NMR and THz/far-IR.
• In situ THz/far-IR spectroscopy revealed dynamic structural changes across crystal, glass, and liquid phases.
• Halogenated ZIF glasses demonstrated enhanced gas-uptake capabilities.

Conclusions:

• Mixed-ligand approaches can yield novel ZIFs with glass-forming properties.
• The melting behavior of ZIFs is linked to the deformability of ZnN4 tetrahedra.
• Incorporating halogenated ligands into MOF glasses enhances their gas adsorption potential.
• These findings provide insights into the structure-property relationships of ZIF glasses.