How to get maximum structure information from anisotropic displacement parameters obtained by three-dimensional...

Area of Science:

• Materials Science
• Crystallography
• Nanotechnology

Background:

• Three-dimensional electron diffraction (3D ED) is crucial for ab initio structure determination of nanocrystals (e.g., metal-organic frameworks, MOFs) too small for single-crystal X-ray diffraction (SCXRD).
• Current 3D ED structure refinements often use isotropic displacement parameters (U_eq), limiting the analysis of atomic disorder and motion.
• Anisotropic displacement parameters (ADPs) offer detailed information on atomic displacements and flexibility, but their interpretation in 3D ED studies, especially for MOFs, is underdeveloped.

Purpose of the Study:

• To conduct a detailed study and interpretation of structure models refined anisotropically against 3D ED data.
• To investigate the influence of data-merging strategies on ADP refinement.
• To propose strategies for obtaining accurate structure models with interpretable ADPs from 3D ED data.

Main Methods:

• Anisotropic structure refinement against 3D ED data for three MOF samples (ZIF-EC1, MIL-140C, Ga(OH)(1,4-ndc)).
• Comparison of ADPs obtained from individual datasets and various data-merging strategies.
• Kinematical refinement approach for obtaining interpretable ADPs.

Main Results:

• Successfully refined and interpreted anisotropic displacement parameters (ADPs) from 3D ED data for selected MOFs.
• Demonstrated that ADPs provide clear and unambiguous information regarding linker motions within the MOFs.
• Identified the impact of different data-merging strategies on the quality and interpretability of refined ADPs.

Conclusions:

• Anisotropic refinement against 3D ED data is a viable method for detailed structural analysis, revealing atomic flexibility and disorder.
• The proposed strategies enable the acquisition of accurate structure models with meaningful ADPs from 3D ED data.
• Interpretable ADPs from 3D ED significantly enhance our understanding of dynamic processes and structural nuances in nanocrystalline materials like MOFs.