Ge Meng, Yang Taimin, Xu Hongyi, Zou Xiaodong, Huang Zhehao
Department of Materials and Environmental Chemistry, Stockholm University, Stockholm SE-106 91, Sweden.
J Am Chem Soc. 2022 Aug 24;144(33):15165-15174. doi: 10.1021/jacs.2c05122. Epub 2022 Aug 11.
In the study of framework materials, probing interactions between frameworks and organic molecules is one of the most important tasks, which offers us a fundamental understanding of host-guest interactions in gas sorption, separation, catalysis, and framework structure formation. Single-crystal X-ray diffraction (SCXRD) is a conventional method to locate organic species and study such interactions. However, SCXRD demands large crystals whose quality is often vulnerable to, e.g., cracking on the crystals by introducing organic molecules, and this is a major challenge to use SCXRD for structural analysis. With the development of three-dimensional electron diffraction (3D ED), single-crystal structural analysis can be performed on very tiny crystals with sizes on the nanometer scale. Here, we analyze two framework materials, SU-8 and SU-68, with organic molecules inside their inorganic crystal structures. By applying 3D ED, with fast data collection and an ultralow electron dose (0.8-2.6 e Å), we demonstrate for the first time that each nonhydrogen atom from the organic molecules can be ab initio located from structure solution, and they are shown as distinct and well-separated peaks in the difference electrostatic potential maps showing high accuracy and reliability. As a result, two different spatial configurations are identified for the same guest molecule in SU-8. We find that the organic molecules interact with the framework through strong hydrogen bonding, which is the key to immobilizing them at well-defined positions. In addition, we demonstrate that host-guest systems can be studied at room temperature. Providing high accuracy and reliability, we believe that 3D ED can be used as a powerful tool to study host-guest interactions, especially for nanocrystals.
在框架材料的研究中，探究框架与有机分子之间的相互作用是最重要的任务之一，这使我们能够从根本上理解气体吸附、分离、催化及框架结构形成过程中的主客体相互作用。单晶X射线衍射（SCXRD）是定位有机物种并研究此类相互作用的传统方法。然而，SCXRD需要大尺寸晶体，而其质量往往容易受到影响，例如引入有机分子时晶体可能会开裂，这是使用SCXRD进行结构分析的一大挑战。随着三维电子衍射（3D ED）的发展，可以对尺寸在纳米级的非常微小的晶体进行单晶结构分析。在此，我们分析了两种框架材料SU - 8和SU - 68，它们的无机晶体结构中含有有机分子。通过应用3D ED，凭借快速的数据收集和超低电子剂量（0.8 - 2.6 e Å），我们首次证明了有机分子中的每个非氢原子都可以从结构解析中从头定位，并且在差分静电势图中显示为清晰且分离良好的峰，具有很高的准确性和可靠性。结果，在SU - 8中为同一客体分子确定了两种不同的空间构型。我们发现有机分子通过强氢键与框架相互作用，这是将它们固定在明确位置的关键。此外，我们证明了可以在室温下研究主客体体系。鉴于具有高准确性和可靠性，我们认为3D ED可作为研究主客体相互作用的有力工具，特别是对于纳米晶体。
