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Covalent organic frameworks (COFs) are a class of crystalline porous organic materials formed by organic structural units connected by covalent bonds. COFs have promising applications due to their permanent porosity, high specific surface areas, tunable pore structures and low mass densities.
Due to the poor reversibility of strong covalent bonds, many cases have shown that COFs cannot form large-sized single-crystal and high-quality microcrystalline powders. So it is difficult to resolve the structures using conventional single-crystal X-ray diffraction (SCXRD) and powder X-ray diffraction (PXRD) methods.
Technical Features – MicroED
MicroED is a structure analysis technique which is developed based on cryo-transmission electron microscopy. The electron diffraction data is collected and analyzed by diffracting electrons from tiny crystals. Extremely small crystal sizes, like micro- and nano-sized crystals, can produce diffraction signals with sufficiently high signal-to-noise ratios. High resolution diffraction data can be provided quickly and efficiently, and it significantly reduces the requirements for sample shape, purity and size.
In 2019, Junliang Sun's group at Peking University and Cheng Wang's group at Wuhan University collaborated to design and synthesize three isostructural 3D COFs with organic groups -H, -Me, and -F. This design was done by fine-tuning the pore environment without changing the topology and the degree of interpenetration. And the crystal structures of these three isostructured 3D COFs were successfully determined by the continuous rotational electron diffraction (cRED) (equivalent to MicroED) technique. These cRED datasets reach a resolution of 0.9-1.0 Å, and for the first time, the positions of all non-hydrogen atoms in the COF framework have been directly determined by the 3D electron diffraction technique.
In 2018, Wei Wang's group at Lanzhou University and Junliang Sun's group at Peking University collaborated to report the first example of interpenetration isomer in COFs, COF-300. The 7-fold interpenetrated diamond structure (dia-c7) of this new isomer was identified by powder X-ray diffraction (PXRD) and rotational electron diffraction (RED) (equivalent to MicroED) analysis.
Reference: Observation of interpenetration isomerism in covalent organic frameworks
Our technical support and commercial colleagues will keep a smooth communication with you throughout the process. After establishing contact with you, we will understand your sample information and requirements in detail, and provide you with the best customized solution.
You need to fill out the Sample Information Form and provide the information required by the technical team for evaluation. For example, providing powder diffraction data and SEM data, the technical team will then provide you with the sample evaluation results and preliminary feasibility program.
3. Sample Delivery
You can choose the appropriate shipping method according to the characteristics of samples.
4.Data Collection and Processing
We will prepare and process the samples according to the characteristics of the samples and the purpose of the experiment. The sample is placed under the electron microscope to find the appropriate sample particles, and series of clear and high quality electron diffraction point images will be collected.
5. Structure Analysis
We will use different algorithms, such as Patterson method, direct method, charge flip method, maximum entropy method, genetic algorithm, simulated annealing method, etc., to resolve the distribution of atoms in the crystal and obtain the initial structure of the crystal. We will further refine the initial structure of the crystal to obtain a chemically reasonable and experimentally observed structure, and finally deliver the results.