Structural Transitions of the Metal-Oxide Nodes within Metal–Organic Frameworks: On the Local Structures of NU-1000 and UiO-66

In
situ pair distribution function (PDF) analyses and density functional
theory (DFT) computations are used to probe local structural transitions
of M6O8 nodes found in two metal organic frameworks
(MOFs), NU-1000 and UiO-66, for M = Zr, Hf. Such transitions are found
to occur without change to the global framework symmetry at temperatures
within a range relevant to many potential MOF applications. For the
particular M6(O)8 nodes studied here, the observed
distortions can be mapped to polymorphic forms known for bulk ZrO2. In the MOF framework, however, node distortions are found
to occur at substantially lower temperature than analogous distortions
in bulk ZrO2 owing to the nanoscale nature of the former.

现场配对分布函数（PDF）分析和密度泛函理论（DFT）计算被应用于探测两种金属有机框架（MOF）中M6O8节点的局部结构转变，这两种MOF分别为NU-1000和UiO-66，其中M代表Zr或Hf。研究发现，这些转变在众多潜在MOF应用的相关温度范围内发生，且不会改变全局框架的对称性。对于此处研究的特定M6(O)8节点，观察到的畸变可以对应到已知的大块ZrO2的多晶型形态。然而，由于前者的纳米尺度特性，MOF框架中的节点畸变出现在比大块ZrO2中类似的畸变温度显著更低的温度下。