The crystal structure of R10Co9In20 (R=Er, Tm, Lu) compounds

New ternary indides R₁₀Co₉In₂₀ (R=Er, Tm, Lu) have been found in the systems {Er, Tm, Lu}–Co–In at 870 K. The crystal structure of Tm₁₀Co₉In₂₀ has been refined using single-crystal X-ray data: Ho₁₀Ni₉In₂₀ structure type, P4/nmm space group, Z=2, a=13.166(5) Å, c=9.097(4) Å, V=1577(2) ų, R=0.0315 for 335 unique reflections hkl (DARTCH-1 diffractometer, MoK_α radiation). The coordination polyhedra of the Tm atoms have 16 and 17 vertices, those of the In atoms 12 and 13 vertices and those of the Co atoms 8 and 10 vertices. The structure can be described as a stacking of polyhedra formed by In atoms.