Four Polyanionic Compounds in the K鈥揂u鈥揋a System: A Case Study in Exploratory Synthesis and of the Art of Structural Analysis

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• 作者：Volodymyr Smetana ; John D. Corbett ; Gordon J. Miller
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：February 6, 2012
• 年：2012
• 卷：51
• 期：3
• 页码：1695-1702
• 全文大小：475K
• 年卷期：v.51,no.3(February 6, 2012)
• ISSN：1520-510X

文摘

The K鈥揂u鈥揋a system has been investigated at 350 掳C for <50 at. % K. The potassium gold gallides K_0.55Au₂Ga₂, KAu₃Ga₂, KAu₂Ga₄ and the solid solution KAu_xGa_3鈥?i>x (x = 0鈥?.33) were synthesized directly from the elements via typical high-temperature reactions, and their crystal structures were determined by single crystal X-ray diffraction: K_0.55Au₂Ga₂ (I, I4/mcm, a = 8.860(3) 脜, c = 4.834(2) 脜, Z = 4), KAu₃Ga₂ (II, Cmcm, a = 11.078(2) 脜, b = 8.486(2) 脜, c = 5.569(1) 脜, Z = 4), KAu₂Ga₄ (III, Immm, a = 4.4070(9) 脜, b = 7.339(1) 脜, c = 8.664(2) 脜, Z = 2), KAu_0.33Ga_2.67 (IV, I-4m2, a = 6.0900(9) 脜, c = 15.450(3) 脜, Z = 6). The first two compounds contain different kinds of tunnels built of puckered six- (II) or eight-membered (I) ordered Au/Ga rings with completely different cation placements: uniaxial in I and III but in novel 2D-zigzag chains in II. III contains only infinite chains of a potassium-centered 20-vertex polyhedron (K@Au₈Ga₁₂) built of ordered 6鈥?鈥? planar Au/Ga rings. The main structural feature of IV is dodecahedral (Au/Ga)₈ clusters. Tight-binding electronic structure calculations by linear muffin-tin-orbital methods were performed for idealized models of I, II, and III to gain insights into their structure鈥揵onding relationships. Density of states curves reveal metallic character for all compounds, and the overall crystal orbital Hamilton populations are dominated by polar covalent Au鈥揋a bonds. The relativistic effects of gold lead to formation of bonds of greater population with most post-transition elements or to itself, and these appear to be responsible for a variety of compounds, as in the K鈥揂u鈥揋a system.