We report a new cyanide-bridged Cs⊂{Fe₄Co₄} box, a soluble model of photomagnetic Prussian blue analogues (PBAs). The Cs⁺ ion has a high affinity for the box and can replace the K⁺ ion in the preformed K-cube. This exchange is kinetically impeded at room temperature but is accelerated by heating and using the 18-crown-6 ether. The inserted Cs⁺ ion confers a high robustness to the cube, which withstands boiling, as shown by variable-temperature NMR studies. The stability of this model complex in solution allows the probing of the electronic interaction between the alkali ion and the cyanide cage by using various techniques. These interactions are known to play a role in the photomagnetic behaviour of PBAs. Firstly, the ¹³³Cs NMR spectroscopy proves that there is an electronic communication between the encapsulated alkali ion and the cyanide cage. The measured up-field signal, observed at ca. −200 ppm at 300 K, reveals that a certain amount of spin density is transferred through the bonds from the paramagnetic Co(II) ion to the encapsulated cation. Secondly, cyclovoltammetric studies show that the nature of the inserted ions affects the redox properties of the cage and influences the electronic communication between the metal ions. However, the differences in the electrochemical properties of the K-cube and the Cs-cube remain moderate. As the switching properties are influenced by the redox potential of the Fe and Co centers, similar photomagnetic behaviour is observed, with both of them being highly photomagnetic. This result contrasts strikingly with previous studies on the 3D polymeric PBAs, where the PBAs with a high amount of Cs⁺ show poor photomagnetic behaviour. In that case, cooperative behaviour likely influences the switching properties. Finally, EPR spectroscopy shows that the K-cube is more anisotropic than the Cs-cube. This difference is reflected in the changes occurring in the slow magnetic relaxation (single molecule magnet behaviour) observed in the two cubes.

中文翻译：

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一种新型的{Fe ₄ Co ₄ }可溶性可切换纳米磁体，其包裹Cs ⁺：增强稳定性和氧化还原柔韧性并调节光磁效应。

我们报告了一个新的氰化桥Cs⊂{Fe ₄ Co ₄ }框，一种光磁普鲁士蓝类似物（PBA）的可溶模型。Cs ⁺离子对盒子具有很高的亲和力，可以取代预制K立方体中的K ⁺离子。这种交换在室温下会受到动力学阻碍，但通过加热和使用18冠6醚会加速这种交换。插入的Cs ⁺可变温度NMR研究表明，离子赋予立方体高的坚固性，可以抵抗沸腾。该模型配合物在溶液中的稳定性允许通过使用各种技术来探测碱金属离子和氰化物笼之间的电子相互作用。已知这些相互作用在PBA的光磁行为中起作用。首先，¹³³ Cs NMR光谱证明，被封装的碱离子与氰化物笼之间存在电子连通。大约在处观察到的测得的场信号。在300 K时为-200 ppm，表明一定量的自旋密度通过顺磁性Co（II）离子到包封的阳离子上。其次，伏安法研究表明，所插入离子的性质会影响笼子的氧化还原特性，并会影响金属离子之间的电子通讯。但是，K-立方体和Cs-立方体的电化学性质的差异仍然适中。由于开关特性受Fe和Co中心的氧化还原电势的影响，因此观察到了相似的光磁行为，两者都具有很高的光磁性。该结果与以前对3D聚合PBA的研究形成鲜明对比，在3D聚合PBA中，Cs ⁺含量较高的PBA表现出不良的光磁行为。在这种情况下，协作行为可能会影响开关性能。最后，EPR光谱表明，K立方比Cs立方更具各向异性。这种差异反映在两个立方体中观察到的慢磁弛豫（单分子磁体行为）中发生的变化中。