Can 3D electron diffraction provide accurate atomic structures of metal-organic frameworks?

Area of Science:

• Materials Science
• Crystallography
• Electron Microscopy

Background:

• Many framework materials like metal-organic frameworks (MOFs) and porous coordination polymers (PCPs) are synthesized as polycrystalline powders.
• These small crystallites are often too small for traditional structure determination methods such as single crystal X-ray diffraction (SCXRD).
• There is a need for alternative methods to determine the atomic structures of these important materials.

Purpose of the Study:

• To demonstrate the utility of three-dimensional (3D) electron diffraction, specifically continuous rotation electron diffraction (cRED), for ab initio structure determination of polycrystalline framework materials.
• To present a complete structural analysis of a biocomposite, Bovine Serum Albumin (BSA) encapsulated in a zeolitic imidazolate framework (ZIF), denoted BSA@ZIF-CO3-1, using cRED.
• To highlight the accuracy and speed of cRED for analyzing framework structures.

Main Methods:

• Utilized continuous rotation electron diffraction (cRED), a 3D electron diffraction technique.
• Employed low electron dose and ultrafast data collection to minimize electron beam damage to the sample.
• Performed ab initio structure determination on a polycrystalline biocomposite sample (BSA@ZIF-CO3-1).

Main Results:

• Successfully determined the complete atomic structure of the BSA@ZIF-CO3-1 biocomposite using cRED.
• Demonstrated that the atomic structure obtained by cRED is as reliable and accurate as that obtained by SCXRD.
• Showcased the feasibility of analyzing materials that are typically challenging for SCXRD due to small crystallite size.

Conclusions:

• Continuous rotation electron diffraction (cRED) is a powerful method for the ab initio structure determination of polycrystalline framework materials.
• The high accuracy and speed of cRED open new avenues for investigating cooperative phenomena in framework structures at the atomic level.
• This technique is particularly valuable for materials synthesized as small powders, overcoming limitations of traditional SCXRD.