Premium
Complex Polyanionic Nets in RbAu 4.01(2) Ga 8.64(5) and CsAu 5 Ga 9 : The Role of Cations in the Formation of New Polar Intermetallics
Author(s) -
Smetana Volodymyr,
Corbett John D.,
Miller Gordon J.
Publication year - 2014
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201400015
Subject(s) - crystallography , gallium , tetragonal crystal system , atom (system on chip) , hexagonal crystal system , alkali metal , intermetallic , crystal structure , electron counting , superstructure , materials science , polyhedron , structure type , type (biology) , chemistry , alloy , physics , geometry , metallurgy , organic chemistry , quantum mechanics , computer science , electron , thermodynamics , embedded system , ecology , mathematics , biology
Two new alkali metal‐poor phases with gold and gallium have been synthesized and structurally characterized using single‐crystal X‐ray diffraction. RbAu 4.01(2) Ga 8.64(5) ( I ) crystallizes in a new tetragonal structure type ( tI 163.8; I 4/ m , a = 8.806(1), c = 40.561(8) Å, 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 NaZn 13 ‐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. CsAu 5 Ga 9 ( II ) crystallizes with a hexagonal unit cell ( hP 30; P 6 3 / mmc , a = 7.635(1), c = 12.279(3) Å, Z = 2) in the BaNi 9 P 5 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@Au 12 Ga 18 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 CsAu 5 Ga 9 indicate that although the average Ga–Ga orbital interactions are optimized at the Fermi level, the specific interactions are not.