Rare‐earth Metal Substitution in Calcium Germanides with the Tetragonal Cr 5 B 3 Type Structure
Rare‐earth Metal Substitution in Calcium Germanides with the Tetragonal Cr 5 B 3 Type Structure
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四方 Cr 5 B 3 型结构的锗化钙中的稀土金属替代
DOI：
10.1002/zaac.202200183
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Bobev, Svilen
中科院分区：
文献类型：
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作者：
Suen, Nian‐Tzu;Bobev, Svilen
具有两种中晚期稀土金属 Ca5−xGdxGe3 和 Ca5−xTbxGe3(x≈0.1−0.2) 的锗化钙已被合成并进行了结构表征。此外，还发现了一种具有钙取代的富镧锗化物 La5−xCaxGe3(x≈0.5)。通过单晶X射线衍射方法建立了这三种结构，并证实在四方空间群I4/mcm（编号140；Z=4；皮尔逊符号tI32）中以Cr5B3型结晶，其中部分锗原子互连成Ge2二聚体，形式为[Ge2]6−。稀土金属和钙原子排列成扭曲的三棱柱、正方反棱柱和立方体，以Ge或稀土/钙金属原子为中心。这些研究表明，取代二价钙原子的三价稀土金属原子的数量与Ge2-二聚体中Ge−Ge键的长度直接相关，距离在Ca5−xGdxGe3中的2.58 Å和La5−xCaxGe3中的2.75 Å之间变化。 Ge−Ge 键的这种伸长与母体 Ca5Ge3Zintl 相（例如 (Ca2+)5[Ge2]6−[Ge4−]）被驱出理想价电子数并进一步减少的概念一致。在此背景下，这项工作证明了具有 Cr5B3 结构类型的锗化物能够适应取代和更宽的价电子数，同时保持其整体结构完整性。
Calcium germanides with two mid‐late rare‐earth metals, Ca5−xGdxGe3and Ca5−xTbxGe3(x≈0.1−0.2), have been synthesized and structurally characterized. Additionally, a lanthanum‐rich germanide with calcium substitutions, La5−xCaxGe3(x≈0.5) has also been identified. The three structures have been established from single‐crystal X‐ray diffraction methods and confirmed to crystallize with the Cr5B3‐type in the tetragonal space groupI4/mcm(no. 140;Z=4; Pearson symboltI32), where part of the germanium atoms are interconnected into Ge2‐dimers, formally [Ge2]6−. Rare‐earth metal and calcium atoms are arranged in distorted trigonal prisms, square‐antiprisms and cubes, centered by Ge or rare‐earth/calcium metal atoms. These studies show that the amount of trivalent rare‐earth metal atoms substituting divalent calcium atoms is in direct correlation with the lengths of the Ge−Ge bond within the Ge2‐dimers, with distance varying between 2.58 Å in Ca5−xGdxGe3and 2.75 Å in La5−xCaxGe3. Such an elongation of the Ge−Ge bond is consistent with the notion that the parent Ca5Ge3Zintl phase (e. g. (Ca2+)5[Ge2]6−[Ge4−]) is being driven out of the ideal valence electron count and further reduced. In this context, this work demonstrates the ability of the germanides with the Cr5B3structure type to accommodate substitutions and wider valence electron count while maintaining their global structural integrity.