Two Iron-Containing Tungstogermanates: [K(H2O)(-Fe2GeW10O37(OH))(-GeW10O36)]12- and [{-Fe2GeW10<

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• 作者：Nadeen H. Nsouli ; Sib Sankar Mal ; Michael H. Dickman ; Ulrich Kortz ; Bineta Keita ; Louis Nadjo ; Juan M. Clemente-Juan
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：October 15, 2007
• 年：2007
• 卷：46
• 期：21
• 页码：8763 - 8770
• 全文大小：268K
• 年卷期：v.46,no.21(October 15, 2007)
• ISSN：1520-510X

文摘

Interaction of the dilacunary polyanion precursor [-GeW₁₀O₃₆]^8- with Fe³⁺ ions in aqueous buffer medium (pH 4.8)results in the formation of two dimeric tungstogermanates depending on the reactant ratios. When using an Fe³⁺to [-GeW₁₀O₃₆]^8- ratio of 1:1, the asymmetric anion [K(H₂O)(-Fe₂GeW₁₀O₃₇(OH))(-GeW₁₀O₃₆)]^12- (1) is formed,whereas [{-Fe₂GeW₁₀O₃₇(OH)₂}₂]^12- (2) is formed when using a ratio of 2:1. Single-crystal X-ray analyses werecarried out on Cs₃K₉[K(H₂O)(-Fe₂GeW₁₀O₃₇(OH))(-GeW₁₀O₃₆)]·19H₂O (CsK-1), which crystallizes in the triclinicsystem, space group P, a = 11.4547(2), b = 19.9181(5), c = 21.0781(6) &Aring;, = 66.7977(12), = 89.1061(12), = 84.4457(11), and Z = 2 and on Cs₇K₄Na[{-Fe₂GeW₁₀O₃₇(OH)₂}₂]·39H₂O (CsKNa-2), which crystallizes inthe monoclinic system, space group C2/m, a = 32.7569(13), b = 12.2631(5), c = 14.2895(5) Å, = 104.135(2),and Z = 2. Polyanion 1 consists of (-Fe₂GeW₁₀O₃₇) and (-GeW₁₀O₃₆) units linked via two Fe-O-W bridges anda central potassium ion. Two equivalent FeO₆ octahedra complete the belt of the -Keggin unit and link to the(-GeW₁₀O₃₆) fragment. On the other hand, 2 consists of two {-Fe₂GeW₁₀O₃₇(OH)₂} units with four bridginghydroxo groups linking the four Fe³⁺ ions, forming an eight-membered ring. The magnetic properties of CsK-1 andCsKNa-2 have been studied by magnetic susceptibility and magnetization measurements and fitted according toan isotropic exchange model. Both polyanions 1 and 2 exhibit diamagnetic ground states with a small amount ofparamagnetic impurity. Electrochemistry studies on 1 and 2 were carried out in a pH 5 acetate medium. The twopolyanions have in common the simultaneous reduction of all of their Fe³⁺ centers. This observation suggests theexistence of identical or almost-identical influences on these centers and their equivalence, especially in the reducedstate. Controlled potential coulometry results indicate the presence of two Fe³⁺ centers in 1 and four in 2. Thesplitting of the tungsten wave of 1 compared to the single tungsten wave of 2 is attributed to a difference inacid-base properties of the polyanions. Voltammetric peak-potential shifts as a function of pH were studied in thecase of 2.