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Abstract：
Although COF-300 is often used as an example to study the synthesis and structure of (3D) covalent organic frameworks (COFs), knowledge of the underlying synthetic processes is still fragmented. Here, an optimized synthetic procedure based on a combination of linker protection and modulation was applied. Using this approach, the influence of time and temperature on the synthesis of COF-300 was studied. Synthesis times that were too short produced materials with limited crystallinity and porosity, lacking the typical pore flexibility associated with COF-300. On the other hand, synthesis times that were too long could be characterized by loss of crystallinity and pore order by degradation of the tetrakis(4-aminophenyl)methane (TAM) linker used. The presence of the degradation product was confirmed by visual inspection, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). As TAM is by far the most popular linker for the synthesis of 3D COFs, this degradation process might be one of the reasons why the development of 3D COFs is still lagging compared with 2D COFs. However, COF crystals obtained via an optimized procedure could be structurally probed using 3D electron diffraction (3DED). The 3DED analysis resulted in a full structure determination of COF-300 at atomic resolution with satisfying data parameters. Comparison of our 3DED-derived structural model with previously reported single-crystal X-ray diffraction data for this material, as well as parameters derived from the Cambridge Structural Database, demonstrates the high accuracy of the 3DED method for structure determination. This validation might accelerate the exploitation of 3DED as a structure determination technique for COFs and other porous materials.
摘要：
尽管COF-300经常被用作研究（3D）共价有机骨架（COF）的合成和结构的示例，对底层合成过程的知识仍然支离破碎。这里,应用了基于接头保护和调节的组合的优化合成程序。使用这种方法，研究了时间和温度对COF-300合成的影响。合成时间太短产生的材料具有有限的结晶度和孔隙率，缺乏与COF-300相关的典型孔隙柔韧性。另一方面,过长的合成时间可以通过使用的四（4-氨基苯基）甲烷（TAM）接头的降解来表征结晶度和孔序的损失。通过目视检查确认降解产物的存在，拉曼光谱和X射线光电子能谱(XPS)。由于TAM是迄今为止最受欢迎的3DCOF合成接头，这种退化过程可能是3DCOF的发展与2DCOF相比仍然滞后的原因之一。然而,通过优化程序获得的COF晶体可以使用3D电子衍射(3DED)在结构上探测。3DED分析导致COF-300在原子分辨率下的完整结构确定，并具有令人满意的数据参数。将我们的3DED衍生的结构模型与先前报道的该材料的单晶X射线衍射数据进行比较，以及来自剑桥结构数据库的参数，证明了3DED方法用于结构测定的高精度。这种验证可能会加速3DED作为COF和其他多孔材料的结构确定技术的开发。
