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Title: Rare‐earth Metal Substitution in Calcium Germanides with the Tetragonal Cr 5 B 3 Type Structure

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.

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Wiley Blackwell (John Wiley & Sons)
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Journal Name:
Zeitschrift für anorganische und allgemeine Chemie
Medium: X
Sponsoring Org:
National Science Foundation
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