Mapping nanocrystalline disorder within an amorphous metal-organic framework.

Area of Science:

• Materials Science
• Nanotechnology
• Chemistry

Background:

• Intentionally disordered metal-organic frameworks (MOFs) exhibit complex functional properties.
• Characterizing the atomic structures of disordered MOFs is a significant challenge.
• X-ray pair distribution function (PDF) methods provide average local structure but miss spatial variations.

Purpose of the Study:

• To characterize the atomic structure of intentionally disordered Fe-BTC MOFs.
• To probe the spatially separated atomic structure of the amorphous matrix in Fe-BTC.
• To quantify disorder at the critical length scale for engineering composite MOF materials.

Main Methods:

• Scanning electron diffraction (SED) to map crystalline and amorphous components and evaluate domain size.
• Electron pair distribution function (ePDF) analysis to probe the amorphous matrix structure.
• Bragg scattering analysis to investigate orientational disorder in nanocrystallites.

Main Results:

• SED successfully mapped crystalline and amorphous phases and determined domain sizes.
• ePDF analysis revealed the atomic structure of the amorphous matrix.
• Bragg scattering showed continuous lattice rotation exceeding 10° in nanocrystallites, indicating significant orientational disorder.
• Candidate unit cells for the crystalline component were identified.

Conclusions:

• This study successfully quantified disorder in Fe-BTC MOFs at the nanoscale.
• The applied electron diffraction techniques are effective for characterizing complex composite MOF structures.
• Understanding and quantifying disorder is essential for the rational design and engineering of advanced MOF materials.