Preparation and structure refinements of Pd2Mg5 and Ir2.096Mg1.980In2.924 with hexagonaICo2Al5 type structure

The intermetallic compounds Pd2Mg5 and Ir2.096Mg1.980In2.924 were prepared from the elements in sealed niobium ampoules in a water-cooled sample chamber of an induction furnace. The compounds were investigated by X-ray diffraction on powders and single crystals: P6(3)/mmc, CoAl5 type, a = 867.1(1), c = 816.4(1) pm, wR2 = 0.0433, 475 F-2 values, 20 parameters for Pd2Mg5, and a = 833.9(1), c = 860.1(1), wR2 = 0.0652, 468 F-2 values, 23 parameters for Ir2.096Mg1.980In2.924. The Pd2Mg5 structure contains two crystallographically independent palladium sites and three magnesium sites. It is best described by a condensation of the polyhedra around the Pd1 and Mg1 atoms. The Mg1 atoms have a cuboctahedral coordination by 6 Pd2 and 6 Mg3 atoms. These cuboctahedra are condensed via common triangular faces, formed by the Pd2 atoms, to columns along 00 z. The Pd1 have a tricapped trigonal prismatic coordination by 6 Mg3 and 3 Mg2 atoms. Also these polyhedra are condensed via common triangular Mg3 faces forming columns extending in 1/3 2/3 z and 2/3 1/3 z The two different columns are connected via common magnesium atoms. In Ir2.096Mg1.980In2.924 two magnesium sites show significant mixing with indium (47-74% indium on the magnesium sites) and additionally the Mg1 site is occupied by 81% In and 19% iridium. Chemical bonding in both intermetallics is briefly discussed. (C) 2004 Elsevier Ltd. All rights reserved.