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Synthesis, Structure, and Bonding in K12Au21Sn4. A Polar Intermetallic Compound with Dense Au20 and Open AuSn4 Layers
Inorganic Chemistry
  • Bin Li, Iowa State University
  • Sung-Jin Kim, Iowa State University
  • Gordon J. Miller, Iowa State University
  • John D. Corbett, Iowa State University
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The new phase K12Au21Sn4 has been synthesized by direct reaction of the elements at elevated temperatures. Single crystal X-ray diffraction established its orthorhombic structure, space group Pmmn (No. 59), a = 12.162(2); b = 18.058(4); c = 8.657(2) Å, V = 1901.3(7) Å3, and Z = 2. The structure consists of infinite puckered sheets of vertex-sharing gold tetrahedra (Au20) that are tied together by thin layers of alternating four-bonded-Sn and -Au atoms (AuSn4). Remarkably, the dense but electron-poorer blocks of Au tetrahedra coexist with more open and saturated Au−Sn layers, which are fragments of a zinc blende type structure that maximize tetrahedral heteroatomic bonding outside of the network of gold tetrahedra. LMTO band structure calculations reveal metallic properties and a pseudogap at 256 valence electrons per formula unit, only three electrons fewer than in the title compound and at a point at which strong Au−Sn bonding is optimized. Additionally, the tight coordination of the Au framework atoms by K plays an important bonding role: each Au tetrahedra has 10 K neighbors and each K atom has 8−12 Au contacts. The appreciably different role of the p element Sn in this structure from that in the triel members in K3Au5In and Rb2Au3Tl appears to arise from its higher electron count which leads to better p-bonding (valence electron concentrations = 1.32 versus 1.22).

Reprinted (adapted) with permission from Inorg. Chem., 2009, 48 (23), pp 11108–11113. Copyright 2009 American Chemical Society.

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Bin Li, Sung-Jin Kim, Gordon J. Miller and John D. Corbett. "Synthesis, Structure, and Bonding in K12Au21Sn4. A Polar Intermetallic Compound with Dense Au20 and Open AuSn4 Layers" Inorganic Chemistry Vol. 48 Iss. 23 (2009) p. 11108 - 11113
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