He Yiwen, De Souza Mattheus, Luo Tian-Yi, Achar Siddarth K, Johnson J Karl, Rosi Nathaniel L
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania, 15260, United States.
Computer Modeling & Simulation Program, University of Pittsburgh, Pittsburgh, Pennsylvania, 15261, United States.
Angew Chem Int Ed Engl. 2024 Oct 14;63(42):e202409150. doi: 10.1002/anie.202409150. Epub 2024 Sep 12.
Incorporating diverse components into metal-organic frameworks (MOFs) can expand their scope of properties and applications. Stratified MOFs (sMOFs) consist of compositionally unique concentric domains (strata), offering unprecedented complexity through partitioning of structural and functional components. However, the labile nature of metal-ligand coordination handicaps achieving compositionally distinct domains due to ligand exchange reactions occurring concurrently with secondary strata growth. To achieve complex sMOF compositions, characterizing and controlling the competing processes of new strata growth and ligand exchange are vital. This work systematically examines controlling ligand exchange in UiO-67 sMOFs by tuning ligand sterics. We present quantitative methods for assessing and visualizing the outcomes of strata growth and ligand exchange that rely on high-angle annular dark-field images and elemental mapping via scanning transmission electron microscopy-energy dispersive X-ray spectroscopy. In addition, we leverage ligand sterics to create 'blocking layers' that minimize ligand exchange between strata which are particularly susceptible to ligand exchange and inter-strata ligand mixing. Finally, we evaluate strata compositional integrity in various solvents and find that sMOFs can maintain their compositions for >12 months in some cases. Collectively, these studies and methods enhance understanding and control over ligand placement in multi-domain MOFs, factors that underscore careful tunning of properties and function.
将多种组分引入金属有机框架（MOF）可以扩展其性能和应用范围。分层金属有机框架（sMOF）由组成独特的同心域（层）构成，通过对结构和功能组分进行划分，提供了前所未有的复杂性。然而，由于配体交换反应与次级层生长同时发生，金属-配体配位的不稳定性质阻碍了获得组成不同的域。为了实现复杂的sMOF组成，表征和控制新层生长与配体交换的竞争过程至关重要。这项工作通过调整配体空间位阻系统地研究了UiO-67 sMOF中配体交换的控制。我们提出了定量方法来评估和可视化层生长与配体交换的结果，这些方法依赖于高角度环形暗场图像以及通过扫描透射电子显微镜-能量色散X射线光谱进行的元素映射。此外，我们利用配体空间位阻创建“阻挡层”，以尽量减少特别容易发生配体交换和层间配体混合的层之间的配体交换。最后，我们评估了各种溶剂中层的组成完整性，发现sMOF在某些情况下可以保持其组成超过12个月。总的来说，这些研究和方法增强了对多域MOF中配体位置的理解和控制，这些因素强调了对性质和功能的精确调节。
