DyIrSn and the Lu3Co2In4-type stannides Sm3Rh2Sn4 and RE 3Ir2Sn4 (RE = Y, Sm, Gd–Tm, Lu)

The Lu3Co2In4-type stannides RE 3Ir2Sn4 (RE = Y, Sm, Gd–Tm, Lu) were synthesized from the elements by arc-melting and subsequent annealing sequences in sealed silica ampoules. For a more comprehensive phase analytical study, the isotypic stannide Sm3Rh2Sn4 and the ZrNiAl-type stannides DyIrSn and LT-YIrSn were also obtained. The polycrystalline samples were characterized through their X-ray powder patterns. The structures of DyIrSn and Gd3Ir2.63(2)Sn3.37(2) (ZrNiAl type, space group P6‾2m), Sm3Ir2.52(2)Sn3.48(1), Gd3Ir2.49(1)Sn3.51(1) and Tm3Ir2.20(3)Sn3.80(3) (Lu3Co2In4 type, space group P6‾) were refined from single-crystal X-ray diffractometer data, revealing residual Ir/Sn disorder in the low-symmetry variants. The RE 3Ir2Sn4 stannides are derived from the equiatomic stannides REIrSn (≍RE 3Rh3Sn3) by partial Ir/Sn substitution. The symmetry reduction from space group P6‾2m to P6‾ is forced by the Ir/Sn ordering within the RE 6 trigonal prisms. The new Sn2 position shows the rare motif of a trigonal planar tin coordination with 289 pm Sn2–Sn1 distances (data for Gd3Ir2.49(1)Sn3.51(1)). 119Sn Mössbauer spectra confirm the two crystallographically independent tin sites in Tm3Ir2Sn4 and the structural disorder in Gd3Ir2Sn4.