Liu Zhi-Kun, Ji Xue-Yang, Yu Meng, Li Yu-Xia, Hu Jie-Sheng, Zhao Yu-Meng, Yao Zi-Shuo, Tao Jun
Key Laboratory of Cluster Science of Ministry of Education, School of Chemistry and Chemical Engineering, Liangxiang Campus, Beijing Institute of Technology, Beijing 102488, P. R. China.
School of Materials Science and Engineering, Shandong Provincial Key Laboratory of Chemical Energy Storage and Novel Cell Technology, Liaocheng University, Liaocheng 252000, P. R. China.
J Am Chem Soc. 2024 Aug 7;146(31):22036-22046. doi: 10.1021/jacs.4c07469. Epub 2024 Jul 23.
Responsive spin-crossover (SCO) metal-organic cages (MOCs) are emerging dynamic platforms with potential for advanced applications in magnetic sensing and molecular switching. Among these, Fe-based MOCs are particularly noteworthy for their air stability, yet they remain largely unexplored. Herein, we report the synthesis of two novel Fe MOCs using a bis-bidentate ligand approach, which exhibit SCO activity above room temperature. These represent the first SCO-active Fe cages and feature an atypical {FeN}-type coordination sphere, uncommon for Fe SCO compounds. Our study reveals that these MOCs are sensitive to acid/base variations, enabling reversible magnetic switching in solution. The presence of multiple active proton sites within these SCO-MOCs facilitates multisite, multilevel proton-induced spin-state modulation. This behavior is observed at room temperature through H NMR spectroscopy, capturing the subtle proton-induced spin-state transitions triggered by pH changes. Further insights from extended X-ray absorption fine structure (EXAFS) and theoretical analyses indicate that these magnetic alterations primarily result from the protonation and deprotonation processes at the NH active sites on the ligands. These processes induce changes in the secondary coordination sphere, thereby modulating the magnetic properties of the cages. The capability of these Fe MOCs to integrate magnetic responses with environmental stimuli underscores their potential as finely tunable magnetic sensors and highlights their versatility as molecular switches. This work paves the way for the development of SCO-active materials with tailored properties for applications in sensing and molecular switching.
响应型自旋交叉（SCO）金属有机笼（MOCs）是新兴的动态平台，在磁传感和分子开关等先进应用方面具有潜力。其中，铁基MOCs因其空气稳定性而特别值得关注，但在很大程度上仍未得到充分探索。在此，我们报告了使用双齿配体方法合成的两种新型铁MOCs，它们在室温以上表现出SCO活性。这些代表了首批具有SCO活性的铁笼，并具有非典型的{FeN}型配位球，这在铁SCO化合物中并不常见。我们的研究表明，这些MOCs对酸碱变化敏感，能够在溶液中实现可逆的磁开关。这些SCO-MOCs中多个活性质子位点的存在促进了多位点、多级质子诱导的自旋态调制。通过核磁共振氢谱在室温下观察到这种行为，捕捉到了由pH变化引发的细微质子诱导自旋态转变。扩展X射线吸收精细结构（EXAFS）和理论分析的进一步见解表明，这些磁学变化主要源于配体上NH活性位点的质子化和去质子化过程。这些过程引起二级配位球的变化，从而调节笼的磁性能。这些铁MOCs将磁响应与环境刺激相结合的能力突出了它们作为精细可调磁传感器的潜力，并彰显了它们作为分子开关的多功能性。这项工作为开发具有定制特性的SCO活性材料以用于传感和分子开关应用铺平了道路。
