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

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 2 m, a = 1618.53(4), c = 919.36(4) pm, wR 2 = 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, wR 2 = 0.0836, 3024 F 2 values, 89 variables for Lu 19.92 Pt 5 In 3 . The platinum compound showed small defects on one lutetium site. Lu 20 Ir 5 In 3 and Lu 20 Pt 5 In 3 are non-centrosymmetric superstructures (through coloring and distortions) that derive from the aristotype Al 5 Co 2 via two steps of symmetry reduction ( P 6 3 / mmc → P 6 3 / mcm → P 2 m ). 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 Ir–Lu contacts that are compatible with substantial Ir–Lu covalent bonding and the structural segregation of In 3 triangles (300 and 315 pm In–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.

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