Magnetic Structure and Exchange Interactions in Quasi-One-Dimensional MnCl2(urea)2

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• 作者：Jamie L. Manson ; Qing-zhen Huang ; Craig M. Brown ; Jeffrey W. Lynn ; Matthew B. Stone ; John Singleton ; Fan Xiao
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：December 21, 2015
• 年：2015
• 卷：54
• 期：24
• 页码：11897-11905
• 全文大小：479K
• ISSN：1520-510X

文摘

MnCl₂(urea)₂ is a new linear chain coordination polymer that exhibits slightly counter-rotated Mn₂Cl₂ rhomboids along the chain-axis. The material crystallizes in the noncentrosymmetric orthorhombic space group Iba2, with each Mn(II) ion equatorially surrounded by four Cl^{鈥?/sup> that lead to bibridged ribbons. Urea ligands coordinate via O atoms in the axial positions. Hydrogen bonds of the Cl路路路H鈥揘 and O路路路H鈥揘 type link the chains into a quasi-3D network. Magnetic susceptibility data reveal a broad maximum at 9 K that is consistent with short-range magnetic order. Pulsed-field magnetization measurements conducted at 0.6 K show that a fully polarized magnetic state is achieved at B_sat = 19.6 T with another field-induced phase transition occurring at 2.8 T. Zero-field neutron diffraction studies made on a powdered sample of MnCl₂(urea)₂ reveal that long-range magnetic order occurs below T_N = 3.2(1) K. Additional Bragg peaks due to antiferromagnetic (AFM) ordering can be indexed according to the Ib鈥?i>a2鈥?magnetic space group and propagation vector 蟿 = [0, 0, 0]. Rietveld profile analysis of these data revealed a N茅el-type collinear ordering of Mn(II) ions with an ordered magnetic moment of 4.06(6) 渭_B (5 渭_B is expected for isotropic S = 5/₂) oriented along the b-axis, i.e., perpendicular to the chain-axis that runs along the c-direction. Owing to the potential for spatial exchange anisotropy and the pitfalls in modeling bulk magnetic data, we analyzed inelastic neutron scattering data to retrieve the exchange constants: J_c = 2.22 K (intrachain), J_a = 鈭?.10 K (interchain), and D = 鈭?.14 K with J > 0 assigned to AFM coupling. This J configuration is most unusual and contrasts the more commonly observed AFM interchain coupling of 1D chains.}