Single-crystal x-ray diffraction structures of covalent organic frameworks.

Area of Science:

• Materials Chemistry
• Crystallography
• Supramolecular Chemistry

Background:

• Crystallization remains a significant challenge in porous covalent organic frameworks (COFs) chemistry.
• Structural characterization of COFs has been primarily limited to modeling and diffraction data analysis, lacking atomic precision.

Purpose of the Study:

• To develop a general procedure for growing large single crystals of three-dimensional imine-based COFs.
• To enable high-resolution structural determination of COFs using single-crystal X-ray diffraction.

Main Methods:

• Developed a general procedure for single-crystal growth of imine-based COFs.
• Utilized single-crystal X-ray diffraction to collect high-resolution data (up to 0.83-angstrom resolution).
• Performed unambiguous structure solution and precise anisotropic refinement.

Main Results:

• Successfully grew large single crystals of COF-300, its hydrated form, COF-303, LZU-79, and LZU-111.
• Achieved atomic precision in deciphering structural characteristics, including interpenetration, guest molecule arrangement, and linker disorder.
• Identified uncommon topologies and reversed imine connectivity with unprecedented detail.

Conclusions:

• The developed method overcomes the crystallization challenge in COF chemistry.
• Single-crystal X-ray diffraction provides definitive structural insights previously unattainable.
• Enables precise understanding of COF structures for advanced material design.