title: Similar K@Au10Sn10 polyhedra in the markedly different structures of KAu4Sn6 and KAu3Sn3. syntheses and characterization.
abstract: These compounds were synthesized by high-temperature reactions of the elements in welded Ta tubes and characterized by X-ray diffraction methods and linear muffin-tin orbital (LMTO) calculations. AAu4Sn6 (A = K, Rb) have a new structural type (Fddd, Z = 8), and KAu3Sn3 (Pmmn, Z = 2) is isostructural with SrAu3In3. Both orthorhombic structures contain similar condensed K@Au10Sn10 polyhedral building blocks, which can be described as overall 6-8-6 arrangements of planar rings or, alternatively, as hexagonal prisms centered by K and augmented about the waists by 8-rings of Au and Sn. However, the 3D Au-Sn networks differ appreciably in both composition and the modes of condensation. In KAu3Sn3, the prisms stack by sharing both hexagonal faces with like neighbors along a, whereas those in KAu4Sn6 condense in a complex zigzag network. Compared with related indium systems, the structure change from KAu4In6 ( P_6m2, Z = 1) to KAu4Sn6 apparently illustrates the effect of complex factors such as atom size and valence electron counts on structure, whereas the SrAu3In3 and KAu3Sn3 pair are isotypic. Both compounds are Pauli-paramagnetic and inert to water at room temperature for several days. Tight-binding electronic structure (LMTO) calculations emphasize the dominance and strength of the heteroatomic Au-Sn bonding.
authors.affiliation: Ames Laboratory-DOE and Department of Chemistry, Iowa State University, Ames, IA 50011, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Li
authors.forename: John D
authors.initials: JD
authors.lastname: Corbett