High pressure synthesis and single-crystal structure refinement of calcium aurate(III), CaAu2O4

Single crystals of calcium aurate(III), CaAu2O4, were obtained by high-pressure treatment of a CaO/Au2O3/KO2 mixture at 40 kbar, 1200 degrees C in a modified Belt-type apparatus. The crystals are tetragonal, space group I4(1)/a, with a = 5.9868(7), c = 10.043(1) Angstrom, c/a = 1.678 and Z = 4. CaAu2O4 is isostructural with LaPd2O4, SrAU(2)O(4) and BaAu2O4. Its structure comprises square-planar AuO4 groups (< Au-O > = 2.007 which are stacked into columns along [100] and [010]. These columns are connected by shared corners forming a three-dimensional framework. The Ca ions are situated in tunnels created by the gold-oxygen partial structure. They are surrounded by eight oxygen atoms (< Ca-O > = 2.490 Angstrom) in a slightly distorted dodecahedron.