Self-assembly-based structural transition has been explored for various applications, including molecular machines, sensors, and drug delivery. In this study, we developed new redox-active metal–organic frameworks (MOFs) called DGIST-10 series that comprise π-acidic 1,4,5,8-naphthalenediimide (NDI)-based ligands and Ni²⁺ ions, aiming to boost ligand-self-assembly-driven structural transition and study the involved mechanism. Notably, during the synthesis of the MOFs, a single-crystal–amorphous–single-crystal structural transition occurred within the MOFs upon radical formation, which was ascribed to the fact that radicals prefer spin-pairing or through-space electron delocalization by π-orbital overlap. The radical-formation-induced structural transitions were further confirmed by the postsynthetic solvothermal treatment of isolated nonradical MOF crystals. Notably, the transient amorphous phase without morphological disintegration was clearly observed, contributing to the seminal structural change of the MOF. We believe that this unprecedented structural transition triggered by the ligand self-assembly magnifies the structural flexibility and diversity of MOFs, which is one of the pivotal aspects of MOFs.

中文翻译：

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自由基驱动的金属-有机框架的晶体-非晶-晶体转变

基于自组装的结构转变已被探索用于各种应用，包括分子机器、传感器和药物输送。在这项研究中，我们开发了称为 DGIST-10 系列的新型氧化还原活性金属有机框架 (MOF)，其包含 π-酸性 1,4,5,8-萘二亚胺 (NDI) 基配体和 Ni ²⁺离子，旨在促进配体自组装驱动的结构转变并研究相关机制。值得注意的是，在 MOF 的合成过程中，自由基形成时 MOF 内部发生了单晶-非晶-单晶结构转变，这归因于自由基更喜欢自旋配对或通过 π- 进行空间电子离域。轨道重叠。通过对分离的非自由基 MOF 晶体进行合成后溶剂热处理，进一步证实了自由基形成诱导的结构转变。值得注意的是，可以清楚地观察到没有形态分解的瞬态非晶相，这促成了 MOF 的重要结构变化。我们认为，配体自组装引发的这种前所未有的结构转变放大了MOF的结构灵活性和多样性，这是MOF的关键方面之一。