Exploring the Role of Cluster Formation in UiO Family Hf Metal-Organic Frameworks with in Situ X-ray Pair Distribution Function Analysis
Exploring the Role of Cluster Formation in UiO Family Hf Metal-Organic Frameworks with in Situ X-ray Pair Distribution Function Analysis
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DOI：
10.1021/jacs.1c06990
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发表时间：
2021-12-01
影响因子：
15
通讯作者：
Cliffe, Matthew J.
中科院分区：
文献类型：
--
作者：
Firth, Francesca C. N.;Gaultois, Michael W.;Cliffe, Matthew J.
金属有机骨架(MOF)结构对合成条件的微小变化非常敏感。影响UIOMOF相结构的一个关键区别是作为骨架节点的Zr或Hf金属团簇的形状和成核能力；尽管这些团簇是至关重要的，但它们在MOF合成过程中的演变还没有完全被理解。在本文中，我们探索了在不同的反应溶液中形成的Hf金属团簇的性质，包括在DMF、甲酸和水的混合物中。我们发现，在UIOMOF合成中，溶剂和反应温度的选择决定了团簇的一致性，从而决定了MOF的结构。利用原位X射线对分布函数测量，我们证明了在UIOMOF合成过程中，可以跟踪不同Hf团簇物种从溶液阶段到全晶体框架的演化，并利用我们的理解提出了HCP UIO-66(HF)MOF的形成机制，在该机制中，金属团簇首先从M-6团簇(如FCuUIO-66)聚集到具有HCP特征的M-12双团簇，然后形成结晶的HCP骨架。这些见解通过调整合成条件以选择不同的簇物种，为合理设计迄今未知的MOF结构的合成铺平了道路。
The structures of Zr and Hf metal-organic frameworks (MOFs) are very sensitive to small changes in synthetic conditions. One key difference affecting the structure of UiO MOF phases is the shape and nuclearity of Zr or Hf metal clusters acting as nodes in the framework; although these clusters are crucial, their evolution during MOF synthesis is not fully understood. In this paper, we explore the nature of Hf metal clusters that form in different reaction solutions, including in a mixture of DMF, formic acid, and water. We show that the choice of solvent and reaction temperature in UiO MOF syntheses determines the cluster identity and hence the MOF structure. Using in situ X-ray pair distribution function measurements, we demonstrate that the evolution of different Hf cluster species can be tracked during UiO MOF synthesis, from solution stages to the full crystalline framework, and use our understanding to propose a formation mechanism for the hcp UiO-66(Hf) MOF, in which first the metal clusters aggregate from the M-6 cluster (as in fcu UiO-66) to the hcp-characteristic M-12 double cluster and, following this, the crystalline hcp framework forms. These insights pave the way toward rationally designing syntheses of as-yet unknown MOF structures, via tuning the synthesis conditions to select different cluster species.