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Abstract An extended series of rare‐earth metal calcium germanides have been synthesized and structurally characterized. The compounds have the general formulaRE5−xCaxGe4(1.5<x<3.6;RE=rare‐earth metal; Ce, Nd, Sm, Tb−Lu) and their structures have been established from single‐crystal X‐ray diffraction methods. They crystallize with the Gd5Si4‐type in the orthorhombic space groupPnma(No. 62;Z=4; Pearson symboloP36), where the germanium atoms are interconnected into two kinds of Ge2‐dimers, formally [Ge2]6−. These studies show that Ca can be successfully incorporated into the hostRE5Ge4structure, whereby trivalent rare‐earth metal atoms can be substituted by divalent calcium atoms. Rare‐earth metal and calcium atoms are arranged in distorted trigonal prisms and cubes, centered by either Ge or Ca atoms. On one of the metal sites, the substitution is preferential and in 9 out of the 10 refined structures, the Wyckoff site 4cis found almost exclusively occupied by Ca. On the other two metal sites the substitution patterns appear to be governed by the mismatch between the size of theRE3+and Ca2+ions. This work further demonstrates the ability for the Gd5Si4structure type to accommodate the substitution of a non‐magnetic element while maintaining the global structural integrity.
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Rare‐earth Metal Substitution in Calcium Germanides with the Tetragonal Cr 5 B 3 Type Structure
Abstract 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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- Award ID(s):
- 2004579
- PAR ID:
- 10383611
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Zeitschrift für anorganische und allgemeine Chemie
- Volume:
- 648
- Issue:
- 23
- ISSN:
- 0044-2313
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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