MAU(2)O(4) (M=SR, BA), THE FIRST OXOAURATES(III) WITH THREE-DIMENSIONAL ANIONIC PARTIAL STRUCTURE [German]

摘要

Two new aurates, BaAu2O4 and SrAu2O4, have been prepared as polycrystalline greenish-brown powders from alkaline earth peroxides and elemental Au by applying an elevated oxygen pressure (gold tubes, T = 873-923 K, p(O-2) = 333 MPa, 3 d). Single crystals of BaAu2O4 are obtained by adding a 3% aqueous hydrogen peroxide solution and decreasing the temperature to 823 K, with otherwise similar conditions. X-Ray single crystal structure determination on BaAu2O4 led to the tetragonal space group I4(1)/a (No. 88) with four formula units per unit cell, which has the dimensions a = 6.4297(4) Angstrom and c = 10.251(2) Angstrom. The crystal structure was determined and refined to a final R value of 1.88% using 240 unique reflections. The crystal structure of the isotypic SrAu2O4 was refined by full profile analysis of powder X-ray diffraction data (a = 6.1830(1) Angstrom, c = 10.1704(2) Angstrom, I4(1)/a, Z = 4, R(1) = 5.88%, and R(pr) = 8.93%). Both aurates(III) are isostructural with LaPd2O4 and contain square planar AuO4 units which are stacked along [1 0 0] and [0 0 1] and connected to a three-dimensional framework by common corners. The alkaline earth ions are coordinated by eight oxygen atoms to form slightly distorted dodecahedra. The aurates(III) are diamagnetic and decompose under normal atmosphere at temperatures above 773 K. (C) 1995 Academic Press, Inc. [References: 23]