Determination of the real structure of multivariate-MOFs

金属有机骨架(MOF)的主要应用是气体分离和储存以及催化。在寻找具有选择性二氧化碳吸收等特定功能的材料时，所谓的多变量(MTV-)MOF被证明是有希望的候选者，因为它们中的一些表现明显好于它们的单变量同系物的混合物。MTV-MOF是由无机团簇或配位球组成的晶体材料，它们通过不同官能化的有机连接物连接在一起。这种材料的平均结构可以通过对布拉格散射的评估来阐明。此外，由于晶体结构中官能团的不规则排列，导致了弥散散射。对扩散散射的解释对于理解连接基排列以及潜在的结构-性质关系是至关重要的。这项研究的主要目的是通过对X射线散射的评价来描述MTV-MOF的真实结构。通过金属盐和不同官能化的有机连接物的一步溶剂热反应，可以得到高质量的MTV-MOF单晶(即具有完整的骨架)。真空下的工作可能是必要的，因为溶剂分子会引起额外的无序。许多单晶MOF的合成路线使用调制器进行晶体生长，理想情况下，在拟议的研究中应避免使用调制器，因为它们可能会并入晶体结构，从而中断周期性，从而导致额外的漫射散射。对于实际结构的分析，用提供高动态范围的探测器收集的同步辐射衍射数据是至关重要的。然后，结构确定包括几个步骤，即从布拉格散射确定平均结构，仔细检查存在的无序类型的平均结构，将衍射图从衍射计空间转换到倒易空间(重建)，以及使用3D-PDF和蒙特卡罗方法分析漫射散射。对平均结构的解释必须极其谨慎，因为随后的漫射分析取决于平均结构测定的结果。虽然3D-PDF适合于得出关于所研究材料中存在的相关性的类型和方向的定性结论，但是可以同时使用3D-PDF和蒙特卡罗方法来进行精化。建议的研究将有助于更好地理解和帮助多变量MOF的结构-性质关系的合理化。

The main applications of metal-organic frameworks (MOFs) are gas separation and storage as well as catalysis. In the search for materials, which have specific functions like selective CO2 uptake, so-called multivariate (MTV-) MOFs turned out to be promising candidates, as some of them perform significantly better than mixtures of their univariate congeners. MTV-MOFs are crystalline materials, which are built of inorganic clusters or coordination spheres, which are connected by differently functionalized organic linkers. The average structure of such materials can be elucidated with the evaluation of the Bragg scattering. In addition, diffuse scattering occurs, which is caused by the irregular arrangement of the functional groups in the crystal structure. The interpretation of the diffuse scattering is crucial for an understanding of the linker arrangement and thus the underlying structure-property relationship. The main goal of the proposed research is the description of the real structure of MTV-MOFs by means of the evaluation of the diffuse X-ray scattering. High-quality single crystals of MTV-MOFs (i.e. with an intact framework) can be obtained by one-step solvothermal reactions of metal salts and differently functionalized organic linkers. Work under vacuum may be necessary, as solvent molecules cause additional disorder. Many synthesis routes for single-crystalline MOFs use modulators for crystal growth, ideally these should be avoided for the proposed research because they may be incorporated in the crystal structures and thus interrupt the periodicity, which causes additional diffuse scattering. For the analysis of the real-structure, synchrotron diffraction data collected with detectors providing a high dynamic range are crucial. The structure determination then comprises several steps, namely the determination of the average structure from the Bragg scattering, scrutinizing the average structure for the types of disorder present, transformation of the diffraction pattern from diffractometer space to reciprocal space (reconstruction) and analysis of the diffuse scattering using both, 3D-PDF and Monte Carlo methods. The elucidation of the average structure has to be performed with extreme care, as the subsequent analysis of the diffuse scattering depends on the results of the average-structure determination. Whereas the 3D-PDF is suited to derive qualitative conclusions regarding the types and directions of correlations present in the material investigated, refinement can be performed using both, 3D-PDF as well as Monte Carlo methods. The proposed research will lead to a better understanding and aid the rationalization of the structure-property relationships of multivariate MOFs.