As a prominent and representative example of flexible metal–organic frameworks (MOFs), DUT-49(Cu) has gained attention due to the unique phenomenon of negative gas adsorption (NGA), originating from an unprecedented structural contraction during the gas adsorption. Herein, postsynthetic metal exchange is demonstrated to afford DUT-49 frameworks with a wide variety of metal cations, e.g., Mn²⁺, Fe²⁺, Ni²⁺, Zn²⁺, Cu²⁺, and Cd²⁺. The single-crystal-to-single-crystal conversion allowed characterization of the new MOFs by single crystal X-ray diffraction, indicating identical structure and topology compared with that of previously explored DUT-49(Cu) framework. This approach is proven successful in achieving Mn–Mn and Cd–Cd dimers, which are rare examples of M–M paddle-wheel SBUs. The relative stability and flexibility of the resulted frameworks are observed to be highly sensitive to the metal ion of the framework, following the trends predicted by the Irving–Williams series. DUT-49(Ni) was recognized as a second material from the DUT-49 series showing adsorption-induced transitions. A sequential increase in framework flexibility from rigid to flexible and from flexible to NGA has been achieved through selective incorporation of metal centers into the structure. Finally, heterometallic structures are formed by selective and controlled exchange of metal ions to finely tune the flexibility and NGA phenomenon of the framework.

中文翻译：

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通过合成后金属交换调节金属-有机框架 DUT-49 的柔韧性和孔隙率

作为柔性金属有机框架（MOF）的突出和代表性例子，DUT-49（Cu）由于气体吸附过程中前所未有的结构收缩产生的负气体吸附（NGA）的独特现象而受到关注。在此，合成后金属交换被证明可提供具有多种金属阳离子的 DUT-49 框架，例如 Mn ²⁺、Fe ²⁺、Ni ²⁺、Zn ²⁺、Cu ²⁺和 Cd ²⁺. 单晶到单晶的转换允许通过单晶 X 射线衍射表征新的 MOF，表明与先前探索的 DUT-49(Cu) 框架相比具有相同的结构和拓扑结构。事实证明，这种方法成功地实现了 Mn-Mn 和 Cd-Cd 二聚体，这是 M-M 桨轮 SBU 的罕见例子。根据 Irving-Williams 系列预测的趋势，观察到所得框架的相对稳定性和柔韧性对框架的金属离子高度敏感。DUT-49(Ni) 被认为是 DUT-49 系列的第二种材料，显示出吸附诱导的转变。通过将金属中心选择性地结合到结构中，已经实现了框架柔性从刚性到柔性以及从柔性到 NGA 的顺序增加。最后，