Abstract Potassium cobalt hexacyanoferrate(II) [K2CoFe(CN)6] is an extremely selective ion exchanger for cesium ions. To examine the atomic level background for the selectivity a computational structural study using DFT modelling was carried out for K2CoFe(CN)6 and for products where Cs has replaced K in the elemental cube cages closest to the surface. In the K-form compound the potassium ions are not in the center of the Co–Fe–CN elementary cube cages closest to the surface but locate about 140 pm from the cube center towards the surface. When cesium ions are exchanged to these potassium ions they locate much deeper from the surface, being only about 70 pm upwards from the cube center. This apparently leads to much stronger bonding of cesium compared to potassium. Once taken up into the outermost cube cages on the surface of the crystallites cesium ions are not able to penetrate further since they are much larger than the electron window between the cubes. Furthermore, they are not able to return to the solution phase either leading to a practically irreversible sorption.

中文翻译：

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钾对六氰基铁酸钴钾(II)原子级结构中铯置换的影响

摘要 六氰基铁酸钴(II) [K2CoFe(CN)6] 是一种对铯离子具有极强选择性的离子交换剂。为了检查选择性的原子级背景，使用 DFT 建模对 K2CoFe(CN)6 和在最接近表面的元素立方笼中用 Cs 代替 K 的产品进行了计算结构研究。在 K 型化合物中，钾离子不在最靠近表面的 Co-Fe-CN 基本立方体笼的中心，而是位于从立方体中心向表面约 140 pm 的位置。当铯离子与这些钾离子交换时，它们位于离表面更深的地方，从立方体中心向上仅约 70 pm。与钾相比，这显然导致铯的键合更强。一旦被吸收到微晶表面的最外面的立方体笼中，铯离子就不能进一步渗透，因为它们比立方体之间的电子窗口大得多。此外，它们既不能返回到溶液相，也不能导致实际上不可逆的吸附。