Zeuner Martin, Pagano Sandro, Matthes Philipp, Bichler Daniel, Johrendt Dirk, Harmening Thomas, Pöttgen Rainer, Schnick Wolfgang
Ludwig-Maximilians-Universität München, Department Chemie und Biochemie, D-81377 München, Germany.
J Am Chem Soc. 2009 Aug 12;131(31):11242-8. doi: 10.1021/ja9040237.
The mixed valence europium nitridosilicate Eu(2)SiN(3) has been synthesized at 900 degrees 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). Eu(2)SiN(3) is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN(4) tetrahedra running parallel [100] with a maximum stretching factor f(s) = 1.0. The compound is isostructural with Ca(2)PN(3) and Rb(2)TiO(3), 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 Eu(2+) and Eu(3+), respectively. (151)Eu Mössbauer spectroscopy of Eu(2)SiN(3) differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu(2+) and Eu(3+) signals over the whole temperature range. The Eu(2+) 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 mu(B)/f.u. and a small contribution of Eu(3+), in accordance with Eu(2+) and Eu(3+) in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at T(C) = 24 K. DFT calculations of Eu(2)SiN(3) reveal a band gap of approximately 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 Eu(2+) and Eu(3+).
在锂熔剂中，以铕和硅二亚胺Si(NH)₂为原料，在900℃下于焊接的钽安瓿中合成了混合价态的氮氮化硅铕Eu₂SiN₃。通过单晶X射线衍射分析确定了黑色材料的结构（Cmca（编号64），a = 542.3(11) pm，b = 1061.0(2) pm，c = 1162.9(2) pm，Z = 8，767个独立反射，37个参数，R₁ = 0.017，wR₂ = 0.032）。Eu₂SiN₃是一种链状硅酸盐，由一维无限非分支的由共角顶SiN₄四面体组成的二聚体链平行于[100]方向排列，最大拉伸因子f(s)=1.0。该化合物与Ca₂PN₃和Rb₂TiO₃同构，是氮氮化硅类中第一个非分支链状硅酸盐的例子。有两个晶体学上不同的铕位点（处于两个不同的Wyckoff位置8f），分别被Eu²⁺和Eu³⁺占据。Eu₂SiN₃的¹⁵¹Eu穆斯堡尔谱明确区分了这两个铕原子，并证实了它们的等原子多重性，显示出在整个温度范围内Eu²⁺和Eu³⁺信号具有恒定比例的静态混合价态。Eu²⁺位点在4.2 K时显示出磁超精细场分裂。磁化率测量表明，在24 K以上呈现居里 - 外斯行为，有效磁矩为7.5 μB/f.u.，且Eu³⁺贡献较小，这与等原子比例的Eu²⁺和Eu³⁺相符。在T(C)=24 K时检测到异常高温下的铁磁有序。Eu₂SiN₃的密度泛函理论（DFT）计算显示带隙约为0.2 eV，这与该化合物的黑色相符。DFT计算和晶格能量计算（MAPLE）都证实了将两个晶体学上独立的Eu位点分别归为Eu²⁺和Eu³⁺。
