Different cation arrangements in au-in networks. Syntheses and structures of six intermetallic compounds in alkali-metal-Au-In systems

Six robust intermetallic compounds with cations in three different tunnel-like structures have been synthesized in alkali-metal-Au-In systems via high-temperature solid-state methods and characterized by X-ray diffraction: AAu(4)-In-6 [A = K (I), Rb (II), P6m2, Z = 1], K-1.76(6) Au6In4 (III, /4/mcm, Z = 4), and A(x)Au(2)In(2) [x approximate to 0.7, A) K (IV), Rb (V), Cs (VI), P4(2)/nmc, Z = 8]. The first type is constructed from a single cage unit: an alkali-metal-centered 21-vertex polyhedron A@Au9In(12) with 6-9-6 arrangement of planar rings. The others contain uniaxial arrays of tunnels built of differently puckered eight- and four-member Au/In rings. The largely different cation distributions depend on the tunnel constitutions and cation sizes. Tight-binding electronic structure calculations by linear muffin-tin-orbital (LMTO) methods were performed for I and idealized III in order to help understand their chemical bonding. These also reveal large differences in relativistic effects for Au d orbitals, as well as for different Au sites in each structure.