Chains of trans

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• 作者：Christian M. Schurz ; Thomas Schleid
• 关键词：Lanthanides ; Nitride chlorides ; Oxide nitride chlorides ; Crystal structures
• 刊名：Journal of Alloys and Compounds
• 出版年：2009
• 出版时间：19 October 2009
• 年：2009
• 卷：485
• 期：1-2
• 页码：110-118
• 全文大小：2072 K

文摘

Single crystals of La₂NCl₃ and Na₂Nd₄ONCl₉ were prepared from LaCl₃, La and NaN₃ or NdCl₃, NdOCl, Nd and NaN₃ (both at 850 °C for 7 d) in silica ampoules by a flux method with NaCl as flux and for the second compound also as sodium source. La₂NCl₃ crystallizes in the orthorhombic system with space group Ibam (no. 72) and four formula units in a unit cell of the dimensions a = 1375.32(9), b = 691.89(5) and c = 618.23(4) pm, while Na₂Nd₄ONCl₉ crystallizes in space group P2₁/m (no. 11) of the monoclinic system with two formula units in a unit cell of the dimensions a = 803.54(6), b = 1134.26(8), c = 928.31(7) pm and β = 107.109(5)°. In both structures the dominating features are trans-edge connected [ZM₄] tetrahedra in chains (M₂NCl₃: M = La, Z = N, x = 3.0; Na₂M₄ONCl₉: M = Nd, Z = (1/2)O + (1/2)N, x = 3.5; superscript e: edge connected). These straight chains run parallel to [0 0 1] in La₂NCl₃ and are connected via trans-edge sharing [(Cl1)La₄]¹¹⁺ tetrahedra in the same way as the [NLa₄]⁹⁺ tetrahedra themselves. The second sort of chloride (Cl2) interconnects the layers of the two different types of chains. As a consequence of the lanthanide contraction the nitride chlorides with the composition M₂NCl₃ (M = La–Nd, Gd) crystallize in two different orthorhombic space groups. La₂NCl₃ is structurally isotypic with Ce₂NCl₃ and Pr₂NCl₃ (space group: Ibam), while Nd₂NCl₃ and Gd₂NCl₃ crystallize similarly, but in space group Pbcn. In Na₂Nd₄ONCl₉ the connection between the zigzag chains of trans-edge shared [ZNd₄]^9.5+ tetrahedra (Z = O and N in a 1:1 molar ratio) appears to be more difficult. They are directly coupled via chloride anions and via Cl⁻–Na⁺–Cl⁻ bridges (CN(Na⁺) = 6) in a three-dimensional framework, so the structure is the same as for Na₂Gd₄ONCl₉. Different influences shape the layout of the individual chains as described in the following paper.