Lu₂₀Ir₅In₃ and Lu₂₀Pt₅In₃ – superstructures of the Al₅Co₂ type by coloring and distortion

Abstract

Dedicated to Professor Caroline Röhr on the Occasion of her 60 th Birthday The lutetium-rich intermetallic compounds Lu 20 Ir 5 In 3 and Lu 20 Pt 5 In 3 were synthesized from the elements in sealed tantalum ampules in an induction furnace. The phase purity of the samples was checked by powder X-ray diffraction. The structures of Lu 20 Ir 5 In 3 and Lu 20 Pt 5 In 3 were refined from single crystal X-ray diffractometer data: P � 62m, a = 1618.53(4), c = 919.36(4) pm, wR2 = 0.0588, 2665 F 2 values, 88 variables for Lu 20 Ir 5 In 3 and a = 1630.58(4), c = 920.43(4) pm, wR2 = 0.0836, 3024 F 2 values, 89 variables for Lu 19.92 Pt 5 In 3 . The platinum compound showed small amounts of defects on one lutetium site. Lu 20 Ir 5 In 3 and Lu 20 Pt 5 In 3 are non-centrosymmetric super-structures (through coloring and distortions) that derive from the aristotype Al 5 Co 2 via two steps of symmetry reduction (P6 3 / mmc!P6 3 /mcm!P � 62m). The structures are discussed together with the coloring variants Y 10 RuCd 3 and Y 9 CoMg 4 on the basis of a group subgroup scheme. Striking features of the Lu 20 Ir 5 In 3 structure are short IrÀ Lu contacts and the structural segregation of In 3 triangles (300 and 315 pm InÀ In) that are solely coordinated by lutetium atoms. Temperature dependent magnetic susceptibility studies of the Lu 20 Ir 5 In 3 and Lu 20 Pt 5 In 3 samples indicate Pauli paramagnetism.