The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties |
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Authors: | Mikhail Ryazanov |
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Institution: | Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart, Germany |
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Abstract: | The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI3 and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln12(C2)3I17-type compounds (C 2/c, a=19.610(1) and 19.574(4) Å, b=12.406(2) and 12.393(3) Å, c=19.062(5) and 19.003(5) Å, β=90.45(3)° and 90.41(3)°, for Pr12(C2)3I17 and Nd12(C2)3I17, respectively). All compounds contain infinite zigzag chains of C2-centered metal atom octahedra condensed by edge-sharing into the tcc]∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd12(C2)3I17 sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln3+)12(C26-)3(I−)17(e−) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd12(C2)3I17, Gd12(C2)3I17 and Dy12(C2)3I17 indicate the coexistence of competing magnetic interactions leading to spin freezing at Tf=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at TN=25 and 29 K, respectively. For Dy12(C2)3I17, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe. |
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Keywords: | Rare earth metal carbide halides Chain-like compounds Magnetism Spin freezing |
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