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Complex Polyanionic Nets in RbAu4.01(2)Ga8.64(5) and CsAu5Ga9: The Role of Cations in the Formation of New Polar Intermetallics

TitleComplex Polyanionic Nets in RbAu4.01(2)Ga8.64(5) and CsAu5Ga9: The Role of Cations in the Formation of New Polar Intermetallics
Publication TypeJournal Article
Year of Publication2014
AuthorsSmetana, V, Corbett, JD, Miller, GJ
JournalZeitschrift Fur Anorganische Und Allgemeine Chemie
Volume640
Pagination790-796
Date Published04
Type of ArticleArticle
ISBN Number0044-2313
Accession NumberWOS:000333697200015
Keywordsalkali, Alkali metals, au-ga system, Bonding, cluster, Crystal structure, crystal-structure, earth, gallium, gold, Intermetallic compounds, nazn13, phases, quasi-crystal
Abstract

Two new alkali metal-poor phases with gold and gallium have been synthesized and structurally characterized using single-crystal X-ray diffraction. RbAu4.01(2)Ga8.64(5) (I) crystallizes in a new tetragonal structure type (tI163.8; I4/m, a = 8.806(1), c = 40.561(8) angstrom, Z = 12). The structure of I contains two types of (defect) icosahedra and three types of Rb-centered distorted snub cubes composed of gold and gallium atoms, so that it is a novel tetragonal superstructure of the defect NaZn13-type structure. The defect icosahedra, which are fully centered by Ga atoms, show distortions that minimize the number of Au-Au contacts as well as having a distribution of vacancies that create 12-atom, 11-atom, and 10-atom polyhedra. CsAu5Ga9 (II) crystallizes with a hexagonal unit cell (hP30; P6(3)/mmc, a = 7.635(1), c = 12.279(3) angstrom, Z = 2) in the BaNi9P5 structure type and is the first intermetallic compound of this type. This structure involves a 3-d network of gold atoms, gallium atoms, and Ga-Ga dimers that form Cs@Au12Ga18 polyhedra, which share hexagonal faces along the c-axis and pentagonal bipyramids in the ab-plane. Its structure shares a resemblance with the hexagonal ZrBeSi structure type. Both compounds exhibit unusually large coordination polyhedra of gold and gallium atoms surrounding each alkali metal with up to 30 near neighbors and a reasonably dense packing. Tight-binding electronic structure calculations on CsAu5Ga9 indicate that although the average Ga-Ga orbital interactions are optimized at the Fermi level, the specific interactions are not.

DOI10.1002/zaac.201400015
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