Ca 2 Ga 4 Ge 6 and Ca 3 Ga 4 Ge 6 : Synthesis, Structure, and Electronic Properties

• Published in: Zeitschrift für anorganische und allgemeine Chemie (1950) Vol. 648; no. 15
• Main Authors: Hodge, Kelsey L., Davis, H. Olivia, Koster, Karl G., Windl, Wolfgang, Moore, Curtis E., Goldberger, Joshua E.
• Format: Journal Article
• Language: English
• Published: 12.08.2022
• ISSN: 0044-2313; 1521-3749
• DOI: 10.1002/zaac.202100342

Abstract During the search for transition metal‐free alkyne hydrogenation catalysts, two new ternary Ca−Ga−Ge phases, Ca 2 Ga 4 Ge 6 ( Cmc 2 1 , a=4.1600(10) Å, b=23.283(5) Å, c=10.789(3) Å) and Ca 3 Ga 4 Ge 6 ( C 2/ m , a=24.063(2) Å, b=4.1987(4) Å, c=10.9794(9) Å, β=91.409(4)°), were discovered. These compounds are isostructural to the previously established Yb 2 Ga 4 Ge 6 and Yb 3 Ga 4 Ge 6 analogues, and according to Zintl‐Klemm counting rules, consist of anionic [Ga 4 Ge 6 ] 4− and [Ga 4 Ge 6 ] 6− frameworks in which every Ga and Ge atom would have a formal octet with no Ga−Ga or Ga−Ge π‐bonding. These compounds are metallic, based on temperature dependent electrical resistivity and thermopower measurements for Ca 3 Ga 4 Ge 6 , along with density functional theory calculations for both phases. Unlike the highly active 13‐layer trigonal CaGaGe phase, these new compounds exhibit minimal activity in the semi/full alkyne hydrogenation of phenylacetylene, which is consistent with previous observations that the lack of a formal octet for framework atoms is essential for catalysis in these Zintl‐Klemm compounds.