Glatz Jana, Jiménez Juan-Ramón, Godeffroy Louis, von Bardeleben Hans Jurgen, Fillaud Laure, Maisonhaute Emmanuel, Li Yanling, Chamoreau Lise-Marie, Lescouëzec Rodrigue
Institut Parisien de Chimie Moléculaire, CNRS UMR 8232, Sorbonne Université, 4 place Jussieu, F-75252 Paris cedex 5, France.
Laboratoire Interface et Systèmes Electrochimiques, CNRS UMR 8235, Sorbonne Université, 4 place Jussieu, F-75252 Paris cedex 5, France.
J Am Chem Soc. 2022 Jun 22;144(24):10888-10901. doi: 10.1021/jacs.2c03421. Epub 2022 Jun 8.
FeCo Prussian blue analogues of general formula ACo[Fe(CN)] are responsive, non-stoichiometric materials whose magnetic and optical properties can be reversibly switched by light irradiation. However, elucidating the critical influence of the inserted alkali ion, A, on the material's properties remains complicated due to their complex local structure. Here, by investigating soluble A ⊂ [Fe-Co] cyanido cubes (A = K, Rb, and Cs), both accurate structural and electronic information could be obtained. First, X-ray diffraction analyses reveal distinct interactions between the inserted A ions and the {Fe-Co} box, which impacts the structural distortion in the cubic framework. These distortions vanish, and a displacement of the small K ion from a corner toward the center is observed, as a cobalt corner Co is oxidized to Co. Second, cyclic voltammetry experiments performed at variable temperatures show distinct splitting of the Co ⇔ Co peak potentials for the different A cations, which can be qualitatively linked to different thermodynamic (standard potentials) and kinetic (energy barriers) parameters associated with the structural reorganization accompanying this redox-coupled spin state change. Moreover, for the first time, photomagnetism was investigated in frozen solution to avoid effects of intermolecular interactions. The results show that the metastable state is stabilized following the trend K > Rb > Cs. The outcome of these studies suggests that the interaction of the inserted alkali ions with the cyanide cage and the structural changes accompanying the electron transfer impact the stability of the photoinduced state and the relaxation temperature: the smaller the cation, the higher the structural reorganization and the associated energy barrier, and the more stable the metastable state.
通式为ACo[Fe(CN)]的铁钴普鲁士蓝类似物是响应性非化学计量材料，其磁性和光学性质可通过光照射进行可逆切换。然而，由于其复杂的局部结构，阐明插入的碱金属离子A对材料性质的关键影响仍然很复杂。在这里，通过研究可溶性A⊂[Fe-Co]氰基立方体（A = K、Rb和Cs），可以获得准确的结构和电子信息。首先，X射线衍射分析揭示了插入的A离子与{Fe-Co}盒之间存在明显的相互作用，这影响了立方框架中的结构畸变。随着钴角Co被氧化为Co，这些畸变消失，并且观察到小K离子从角向中心的位移。其次，在可变温度下进行的循环伏安实验表明，不同A阳离子的Co⇔Co峰电位有明显分裂，这可以定性地与伴随这种氧化还原耦合自旋态变化的结构重组相关的不同热力学（标准电位）和动力学（能垒）参数联系起来。此外，首次在冷冻溶液中研究了光磁效应以避免分子间相互作用的影响。结果表明，亚稳态按照K>Rb>Cs的趋势得到稳定。这些研究结果表明，插入的碱金属离子与氰化物笼的相互作用以及伴随电子转移的结构变化影响光诱导态的稳定性和弛豫温度：阳离子越小，结构重组和相关能垒越高，亚稳态越稳定。
