To What Extent Does the Zintl−Klemm Formalism Work? The Eu(Zn1−xGex)2 Series

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• 作者：Tae-Soo You ; Sven Lidin ; Olivier Gourdon ; Yaqiao Wu ; Gordon J. Miller
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：July 20, 2009
• 年：2009
• 卷：48
• 期：14
• 页码：6380-6390
• 全文大小：989K
• 年卷期：v.48,no.14(July 20, 2009)
• ISSN：1520-510X

文摘

The series of ternary polar intermetallics Eu(Zn_1−xGe_x)₂ (0 ≤ x ≤ 1) has been investigated and characterized by powder and single-crystal X-ray diffraction as well as physical property measurements. For 0.50(2) ≤ x < 0.75(2), this series shows a homogeneity width of hexagonal AlB₂-type phases (space group P6/mmm, Pearson symbol hP3) with Zn and Ge atoms statistically distributed in the planar polyanionic 6³ nets. As the Ge content increases in this range, a decreases from 4.3631(6) Å to 4.2358(6) Å, while c increases from 4.3014(9) Å to 4.5759(9) Å, resulting in an increasing c/a ratio. Furthermore, the Zn−Ge bond distance in the hexagonal net drops from 2.5190(3) Å to 2.4455(3) Å, while the anisotropy of the displacement ellipsoids significantly increases along the c direction. For x < 0.50 and x > 0.75, respectively, orthorhombic KHg₂-type and trigonal EuGe₂-type phases occur as a second phase in mixtures with an AlB₂-type phase. Diffraction of the x = 0.75(2) sample shows incommensurate modulation along the c direction; a structural model in super space group P31(00γ)00s reveals puckered 6³ nets. Temperature-dependent magnetic susceptibility measurements for two AlB₂-type compounds show Curie−Weiss behavior above 40.0(2) K and 45.5(2) K with magnetic moments of 7.98(1) μ_B for Eu(Zn_0.48Ge_0.52(2))₂ and 7.96(1) μ_B for Eu(Zn_0.30Ge_0.70(2))₂, respectively, indicating a (4f)⁷ electronic configuration for Eu atoms (Eu²⁺). The Zintl−Klemm formalism accounts for the lower limit of Ge content in the AlB₂-type phases but does not identify the observed upper limit. In a companion paper, the intrinsic relationships among chemical structures, compositions, and electronic structures are analyzed by electronic structure calculations.