Unravelling Crystal Structures of Covalent Organic Frameworks by Electron Diffraction Tomography

Abstract

Featuring the art of covalent chemistry on 2D and 3D with molecular precision, covalent organic frameworks (COFs) have attracted immense interests from inorganic, organic, polymer, materials and energy chemistry. However, due to the synthetic challenge of “crystallization problem”, structural determination of COFs has been the bottle‐neck in speeding up their discovery and design, as well as building up their structure‐ property relation. Electron diffraction tomography (EDT) has been developed to determine crystal structures of COFs with only sub‐micrometer sized single crystals, which enabled the ab initio determination of crystal structure, molecular connectivity, pore metrics, and host‐guest interaction at the atomic level. In this review, we summarized the recent developments of EDT for addressing challenges in structure determinations of such e‐beam sensitive, organic porous crystals, covering comprehensively automatic data collection, low dose, cryogenic protocols, structural solution method, powder X‐ray diffraction refinement, and high‐resolution transmission electron microscopy (HRTEM) imaging techniques. We do believe the EDT will propel this field into the new era of COF chemistry with atomic precision, and we envision the wide application of artificial intelligence will promote the structural determination and particle analysis of COFs and related materials.

Surfactants Mediated Synthesis of Highly Crystalline Thin Films of Imine‐Linked Covalent Organic Frameworks on Water Surface

“…Moreover, the generated films with high crystallinity made it possible to observe into the structure of the COF‐2,5‐Ph by high‐resolution transmission electron microscope (HRTEM). [ 51 ] HRTEM images revealed a clearly visible predicted square lattice (Figure 4j), which is consistent with the simulated COF‐2,5‐Ph structure obtained by Material Studio (Figure 4k). Notably, The SHS‐COF‐2,5‐Ph films maintain good crystallinity at 0.1—2 mol/L PTSA aquous solution, demonstrating surfactant SHS has good adaptability for the formation of highly crystalline COF films under different acidic reaction conditions.…”

Reticular design and crystal structure determination of covalent organic frameworks

“…Details of the historical development of ED have been recently discussed in the literature. 60,61 To date, ED techniques applied for COF structure determinations include two common methods for collecting data: rotation electron diffraction (RED) and continuous rotation electron diffraction (cRED). Zhou and Huang at Stockholm University and Terasaki and Ma at ShanghaiTech University are widely known for their expertise in solving crystal structures of reticular materials using the ED techniques.…”

Synthesis of Thin Film of a Three‐Dimensional Covalent Organic Framework as Anti‐counterfeiting Label

“…[ 12 ] COFs are usually obtained as unprocessable particles under solvothermal conditions or sub‐monolayers from sublimation of monomers onto metal surface under vacuum conditions. [ 13 ] The limited usefulness of these forms prevents the application of COFs in areas, where their reliable contact with electrodes is required such as in electronics and optoelectronics. [ 14 ] Recently, thin films of 2D COFs have been reported through interfacial synthesis at a gas‐liquid interface, [ 15‐16 ] liquid‐ liquid interface, [ 17 ] liquid‐solid interface, [ 18 ] spin coating, [ 19 ] microwave‐assisted synthesis, [ 20 ] and screen printing.…”