Synthesis and crystal structures of the pseudobinary intermetallics IrIn2-xMgx with orthorhombic Mg2Cu structure and IrMg3-xInx with hexagonal Cu3P type

The intermetallic compounds IrIn2-xMgx (x=0.53, 0.70) and Mg3-xInxIr (x=0.80, 0.97) were synthesized by induction melting of the elements in glassy carbon crucibles in a water-cooled sample chamber. All compounds were investigated by X-ray powder diffraction and the structures have been refined on the basis of single-crystal diffractometer data: Mg2Cu type, Fddd, a=981.9(3), b=528.8(1), c=1799.2(4) pm, wR2=0.0620, 507 Fo2 values, 19 variables for IrIn1.47Mg0.53, a=980.8(1), b=528.1(1), c=1797.3(3) pm, wR2=0.0924, 502 Fo2 values, 19 variables for IrIn1.30Mg0.70, and Cu3P type, P63cm, a=788.7(2), c=836.6(2) pm, wR2=0.0403, 715 Fo2 values, 29 variables for Mg2.03In0.97Ir, a=788.6(1), c=832.7(2) pm, wR2=0.0407, 489 Fo2 values, 30 variables for Mg2.20In0.80Ir. The Mg2Cu type structure of IrIn2 has two crystallographically different indium sites which both show mixed In/Mg occupancy. For both crystals a higher magnesium substitution occurs for the In1 site. In the Cu3P type structure of Mg2.03In0.97Ir and Mg2.20In0.80Ir, all four magnesium sites show Mg/In mixing. The by far highest indium occupancy is observed for the Mg1 sites, i.e. 59% in Mg2.03In0.97Ir and 50% in Mg2.20In0.80Ir. The crystal chemistry of these intermetallic compounds is briefly discussed. [Copyright &y& Elsevier]