Pitfalls in metal-organic framework crystallography: towards more accurate crystal structures

Area of Science:

• Materials Science
• Crystallography
• Chemistry

Background:

• Single crystal X-ray diffraction (SC-XRD) is the primary technique for elucidating metal-organic framework (MOF) crystal structures.
• Accurate structure determination is crucial for understanding MOF properties and applications.
• Challenges in MOF crystallography include handling pore-occupying guest molecules and crystallographic twinning.

Purpose of the Study:

• To provide a tutorial on best practices for handling MOF crystals and analyzing SC-XRD data.
• To highlight the critical impact of pore-occupying entities and crystallographic twinning on MOF structure quality.
• To emphasize the importance of addressing these issues for reliable MOF structure determination and reporting.

Main Methods:

• Detailed examination of SC-XRD data analysis specific to MOFs.
• Focus on the proper treatment of pore-occupying guest molecules within crystal structures.
• Guidance on identifying and managing crystallographic twinning in MOF samples.

Main Results:

• Proper sample handling and data analysis can minimize reliance on computational solvent masking techniques (e.g., SQUEEZE).
• Addressing pore occupants and twinning directly improves the quality and reliability of determined MOF crystal structures.
• The presented methodologies are applicable to other porous crystalline materials.

Conclusions:

• Effective management of pore occupants and crystallographic twinning is essential for maintaining SC-XRD's role in MOF structure determination.
• Adherence to these practices ensures higher quality and more trustworthy crystal structures.
• This work aims to enhance the rigor and reproducibility of MOF crystallography.