Iridium-rich silicides <i>RE</i> ₅Ir₁₉Si₁₂ (<i>RE</i> = Y, Gd–Dy, Er, Tm, Lu) with Sc₅Co₁₉P₁₂-type structure

Abstract The Sc 5 Co 19 P 12 -type silicides RE 5 Ir 19 Si 12 ( RE = Y, Gd–Dy, Er, Tm, Lu) were synthesized by arc-melting of the elements and subsequent annealing of the product samples at T = 870 K for one week. The polycrystalline samples were characterized by powder X-ray diffraction. The structure of Tm 5 Ir 19 Si 12 was refined from single-crystal X-ray diffractometer data: hexagonal space group P 6‾2 m , a = 1,269.70(4), c = 393.17(1) pm, w R 2 = 0.0486, 847 F 2 values and 45 variables. The iridium and silicon atoms form a rigid covalently bonded three-dimensional [Ir 19 Si 12 ] substructure with Ir–Ir and Ir–Si distances ranging from 279 to 291 pm and 229–279 pm, respectively. The two crystallographically independent thulium atoms fill larger cavities within the [Ir 19 Si 12 ] substructure. They have coordination numbers of 16 and 15. The silicides RE 5 Ir 19 Si 12 belong to the large family of metal-rich structures with a ratio of metal to p -element of 2:1. The geometry of the structure can be explained by condensation of three different types of silicon-centered trigonal prisms built by the thulium and iridium atoms.