Structure Characterization and Properties of K-Containing Copper Hexacyanoferrate

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• 作者：Dickson O. Ojwang ; Jekabs Grins ; Dariusz Wardecki ; Mario Valvo ; Viktor Renman ; Lennart Häggström ; Tore Ericsson ; Torbjörn Gustafsson ; Abdelfattah Mahmoud ; Raphaël P. Hermann ; Gunnar Svensson
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：June 20, 2016
• 年：2016
• 卷：55
• 期：12
• 页码：5924-5934
• 全文大小：604K
• 年卷期：0
• ISSN：1520-510X

文摘

Copper hexacyanoferrate, Cu^II[Fe^III(CN)₆]_2/3·nH₂O, was synthesized, and varied amounts of K⁺ ions were inserted via reduction by K₂S₂O₃ (aq). Ideally, the reaction can be written as Cu^II[Fe^III(CN)₆]_2/3·nH₂O + 2x/3K⁺ + 2x/3e^– ↔ K_2x/3Cu^II[Fe^II_xFe^III_1–x(CN)₆]_2/3·nH₂O. Infrared, Raman, and Mössbauer spectroscopy studies show that Fe^III is continuously reduced to Fe^II with increasing x, accompanied by a decrease of the a-axis of the cubic Fm3̅m unit cell. Elemental analysis of K by inductively coupled plasma shows that the insertion only begins when a significant fraction, ∼20% of the Fe^III, has already been reduced. Thermogravimetric analysis shows a fast exchange of water with ambient atmosphere and a total weight loss of ∼26 wt % upon heating to 180 °C, above which the structure starts to decompose. The crystal structures of Cu^II[Fe^III(CN)₆]_2/3·nH₂O and K_2/3Cu[Fe(CN)₆]_2/3·nH₂O were refined using synchrotron X-ray powder diffraction data. In both, one-third of the Fe(CN)₆ groups are vacant, and the octahedron around Cu^II is completed by water molecules. In the two structures, difference Fourier maps reveal three additional zeolitic water sites (8c, 32f, and 48g) in the center of the cavities formed by the −Cu–N–C–Fe– framework. The K-containing compound shows an increased electron density at two of these sites (32f and 48g), indicating them to be the preferred positions for the K⁺ ions.