Polar Alignment of Λ-Shaped Basic Building Units within Transition Metal Oxide Fluoride Materials

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• 作者：Michael Holland ; Martin D. Donakowski ; Eric A. Pozzi ; Andrew M. Rasmussen ; Thanh Thao Tran ; Shannon E. Pease-Dodson ; P. Shiv Halasyamani ; Tamar Seideman ; Richard P. Van Duyne ; Kenneth R. Poeppelmeier
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：January 6, 2014
• 年：2014
• 卷：53
• 期：1
• 页码：221-228
• 全文大小：365K
• ISSN：1520-510X

文摘

A series of pseudosymmetrical structures of formula K₁₀(M₂O_nF_11鈥?i>n)₃X (M = V and Nb, n = 2, X = (F₂Cl)_1/3, Br, Br_4/2,I_4/2; M = Mo, n = 4, X = Cl, Br_4/2, I_4/2) illustrates generation of polar structures with the use of 螞-shaped basic building units (BBUs). For a compound to belong to a polar space group, dipole moments of individual species must be partially aligned. Incorporation of d⁰ early transition metal polyhedral BBUs into structures is a common method to create polar structures, owing to the second-order Jahn鈥揟eller distortion these polyhedra contain. Less attention has been spent examining how to align the polar moments of BBUs. To address alignment, we present a study on previously reported bimetallic BBUs and synthesized compounds K₁₀(M₂O_nF_11鈥?i>n)₃X. These materials differ in their (non)centrosymmetry despite chemical and structural similarities. The vanadium compounds are centrosymmetric (space groups P3̅m1 or C2/m) while the niobium and molybdenum heterotypes are noncentrosymmetric (Pmn2₁). The difference in symmetry occurs owing to the presence of linear, bimetallic BBUs or 螞-shaped bimetallic BBUs and related packing effects. These 螞-shaped BBUs form as a consequence of the coordination environment around the bridging anion of the metal oxide fluoride BBUs.