MAU(2)O(4) (M=SR, BA), THE FIRST OXOAURAT ES(III) WITH 3-DIMENSIONAL ANIONIC PARTIAL STRUCTURE

Two new aurates, BaAu2O4 and SrAu2O4, have been prepared as polycrysta lline greenish-brown powders from alkaline earth peroxides and element al 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 tem perature to 823 K, with otherwise similar conditions. X-Ray single cry stal structure determination on BaAu2O4 led to the tetragonal space gr oup 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 1.8 8% using 240 unique reflections. The crystal structure of the isotypic SrAu2O4 was refined by full profile analysis of powder X-ray diffract ion 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 isostruct ural with LaPd2O4 and contain square planar AuO4 units which are stack ed along [1 0 0] and [0 0 1] and connected to a three-dimensional fram ework by common corners. The alkaline earth ions are coordinated by ei ght oxygen atoms to form slightly distorted dodecahedra. The aurates(I II) are diamagnetic and decompose under normal atmosphere at temperatu res above 773 K. (C) 1995 Academic Press, Inc.