Jiménez J-R, Tricoire M, Garnier D, Chamoreau L-M, von Bardeleben J, Journaux Yves, Li Yanling, Lescouëzec R
Sorbonne Universités, UPMC Paris 6, Institut Parisien de Chimie Moléculaire, CNRS UMR 8232, 4 place Jussieu, Paris 75252, France.
Dalton Trans. 2017 Nov 14;46(44):15549-15557. doi: 10.1039/c7dt02989f.
We report a new cyanide-bridged Cs⊂{FeCo} 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 Cs 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.
我们报道了一种新型的氰基桥联Cs⊂{FeCo}盒，它是光磁普鲁士蓝类似物（PBAs）的可溶模型。Cs离子对该盒具有高亲和力，能够取代预制K立方体中的K离子。这种交换在室温下动力学受阻，但通过加热和使用18-冠-6醚可加速。插入的Cs离子赋予立方体高稳定性，如变温核磁共振研究所示，它能经受住沸腾。该模型配合物在溶液中的稳定性使得可以通过各种技术探测碱金属离子与氰化物笼之间的电子相互作用。已知这些相互作用在PBAs的光磁行为中起作用。首先，Cs核磁共振光谱证明封装的碱金属离子与氰化物笼之间存在电子通信。在300 K时约-200 ppm处测得的上移信号表明，一定量的自旋密度通过键从顺磁性Co(ii)离子转移到封装的阳离子上。其次，循环伏安研究表明，插入离子的性质影响笼的氧化还原性质，并影响金属离子之间的电子通信。然而，K立方体和Cs立方体的电化学性质差异仍然适中。由于开关性质受Fe和Co中心的氧化还原电位影响，观察到它们具有相似的光磁行为，二者都具有高光磁性。这一结果与之前对三维聚合PBAs的研究形成了鲜明对比，在之前的研究中，含有大量Cs的PBAs光磁行为较差。在那种情况下，协同行为可能会影响开关性质。最后，电子顺磁共振光谱表明，K立方体比Cs立方体更具各向异性。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）的变化上。
