Structure and Magnetism of Sr3Co2O4Cl2鈥擜n Electronically Driven Lattice Distortion in an Oxychloride Containing Square Planar CoII Centers

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• 作者：Fabio Denis Romero ; Lucy Coyle ; Michael A. Hayward
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：September 26, 2012
• 年：2012
• 卷：134
• 期：38
• 页码：15946-15952
• 全文大小：387K
• 年卷期：v.134,no.38(September 26, 2012)
• ISSN：1520-5126

文摘

Topochemical reduction of Sr₃Co₂O₅Cl₂ with NaH at 200 掳C yields Sr₃Co₂O₄Cl₂, a phase consisting of infinite double sheets of corner-linked Co^IIO₄ square planes stacked with SrCl rocksalt layers. At 298 K, the structure of Sr₃Co₂O₄Cl₂ is described in the tetragonal space group I4/mmm [a = 4.007(1) 脜, c = 22.282(1) 脜]; however, on cooling below 200 K, the structure undergoes a lattice distortion to adopt a structure with orthorhombic symmetry in space group Immm [a = 3.9757(5) 脜, b = 4.0294(5) 脜, and c = 22.147(3) 脜 at 5 K]. The structural distortion can be considered Jahn鈥揟eller-like as it lifts the orbital degeneracy of the square planar, d⁷, Co^II centers, demonstrating a strong coupling between the electronic configuration and the structural lattice of this oxychloride phase. On cooling below 50 K, Sr₃Co₂O₄Cl₂ adopts a canted antiferromagnetically ordered state. All magnetization data show that the local cobalt moment is much greater than would be expected for a simple spin-only S = ³/₂ center, indicating a strong orbital contribution to the magnetic behavior.