Mixed Valence Europium Nitridosilicate Eu2SiN3

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• 作者：Martin Zeuner ; Sandro Pagano ; Philipp Matthes ; Daniel Bichler ; Dirk Johrendt ; Thomas Harmening ; Rainer Pttgen ; Wolfgang Schnick
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：August 12, 2009
• 年：2009
• 卷：131
• 期：31
• 页码：11242-11248
• 全文大小：283K
• 年卷期：v.131,no.31(August 12, 2009)
• ISSN：1520-5126

文摘

The mixed valence europium nitridosilicate Eu₂SiN₃ has been synthesized at 900 °C in welded tantalum ampules starting from europium and silicon diimide Si(NH)₂ in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a = 542.3(11) pm, b = 1061.0(2) pm, c = 1162.9(2) pm, Z = 8, 767 independent reflections, 37 parameters, R1 = 0.017, wR2 = 0.032). Eu₂SiN₃ is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN₄ tetrahedra running parallel [100] with a maximum stretching factor f_s = 1.0. The compound is isostructural with Ca₂PN₃ and Rb₂TiO₃, and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu²⁺ and Eu³⁺, respectively. ¹⁵¹Eu Mssbauer spectroscopy of Eu₂SiN₃ differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu²⁺ and Eu³⁺ signals over the whole temperature range. The Eu²⁺ site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie−Weiss behavior above 24 K with an effective magnetic moment of 7.5 μ_B/f.u. and a small contribution of Eu³⁺, in accordance with Eu²⁺ and Eu³⁺ in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at T_C = 24 K. DFT calculations of Eu₂SiN₃ reveal a band gap of 0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu²⁺ and Eu³⁺.