Transition Metal-Indium Substitution in Y3Rh2-type Compounds

Abstract

New rare earth metal-rich indium compounds RE3T2−xInx (RE = Gd, Tb, Dy, Ho, Er, Tm; T = Rh, Pd, Ir) were synthesized from the elements via high-frequency melting and subsequent annealing in sealed silica ampoules. These intermetallics crystallize with substitution variants of the tetragonal Y3Rh2-type structure, space group I4/mcm, Z = 28. All samples were studied by powder and single crystal X-ray diffraction: a = 1164.2(2), c = 2486.5(5) pm, for Tb3Rh1.25In0.71, a = 1139.4(2), c = 2480.8(5) pm for Er3Rh1.48In0.52, a = 1153.7(2), c = 2465.4(5) pm for Tm3Rh1.25In0.71, a = 1146.4(2), c = 2498.4(5) pm for Tb3Ir1.62In0.33, a = 1154.9(2), c = 2500.1(5) pm for Tb3Ir1.52In0.44, a = 1187.8(2), c = 2559.2(5) pm for Gd3Pd1.27In0.71, and a = 1169.1(2), c = 2530.3(5) pm for Ho3Pd1.27In0.71. The indium atoms show different site occupancies on the transition metal positions, and for most crystals small defects occur for one transition metal site. Gd3Rh1.30In0.64 (a = 1166.3(2), c = 2512.0(5) pm) and Dy3Rh1.31In0.64 reveal complete rhodium-indium ordering. These two indides crystallize with the translationengleiche subgroup I4/m. The rare earth atoms in these RE3T2−xInx indides have coordination numbers between 13 and 15. A striking structural motif is the tetrahedral indium coordination in the first coordination sphere of the RE5 position (305 pm Gd-In in Gd3Rh1.30In0.64). The transition metal atoms show trigonal prismatic or square anti-prismatic rare earth coordination. In all compounds investigated, the indium atoms substitute these metals only at the square prismatic sites and at one site of coordination number 10. The crystal chemical consequences of the different ordered and statistical transition metal-indium substitutions are discussed