Ternary Scandium-rich Indides Sc50T13In3 and Sc50Rh13In3Oy (T = Rh, Ir; y ≈ 8) – Synthesis and Crystal Structure

Abstract

New intermetallic compounds Sc50Rh13.3In2.7 and Sc50Ir13.6In2.4 and the suboxides Sc49.2Rh13In3.8O8.8 and Sc49.2Rh13.7In2.8O8.0 were synthesized from the elements or with Sc2O3 as an oxygen source, respectively, in sealed tantalum tubes in a water-cooled sample chamber of an induction furnace. They crystallize with a new cubic structure type, space group Fm3̅, a = 1772.5(6) pm, wR2 = 0.032, 1111 F2 values, 34 variables for Sc50Rh13.3In2.7, a = 1766.5(6) pm, wR2 = 0.041, 745 F2 values, 34 variables for Sc50Ir13.6In2.4, a = 1764.4(2) pm, wR2 = 0.044, 690 F2 values, 41 variables for Sc49.2Rh13In3.8O8.8, and a = 1761.5(6) pm, wR2 = 0.054, 740 F2 values, 42 variables for Sc49.2Rh13.7In2.8O8.0. The main structural motifs are rhodium-centered indium cubes in an fcc like arrangement in which the octahedral and tetrahedral voids are filled by In2Sc12 and In1Sc12 icosahedra, respectively, resembling a Li3Bi-like structure. The Rh1 (Ir1) and Sc4 atoms lie between these polyhedral units. The oxygen atoms partially fill Sc6 octahedra in Sc49.2Rh13In3.8O8.8 and Sc49.2Rh13.7In2.8O8.0 with Sc-O distances of 214 - 230 pm. These octahedra are condensed via common edges and faces, encapsulating the In2Sc12 icosahedra. Due to the high scandium content one observes strong Sc-Sc bonding with Sc-Sc distances ranging from 303 to 362 pm in Sc49.2Rh13In3.8O8.8. The shortest distances occur for Sc-Rh (267 - 295 pm). The crystal chemical relationship with the Li3Bi-related suboxide Ti12Sn3O10 is discussed.