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:  AAu₄In₆ [A = K (I), Rb (II), P6̄m2, Z = 1], K_1.76(6)Au₆In₄ (III, I4/mcm, Z = 4), and A_xAu₂In₂ [x ≈ 0.7, A = K (IV), Rb (V), Cs (VI), P4₂/nmc, Z = 8]. The first type is constructed from a single cage unit:  an alkali-metal-centered 21-vertex polyhedron A@Au₉In₁₂ 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.