The stannides YbPtSn and Yb2Pt3Sn5

YbPtSn and Yb2Pt3Sn5 were prepared from the elements in sealed tantalum tub es in a high-frequency furnace in a novel water-cooled sample chamber. Both structures were refined from single-crystal X-ray data: YbPtSn (ZrNiAl typ e structure), space group P (6) over bar 2m, a = 737.8(3) pm, c = 393.1(2) pm, wR2 = 0.0363, 412 F-2 values, 14 variables; Yb2Pt2Sn5 (new structure ty pe), space group Pnma, a = 729.5(2) pm, b = 442.2(1) pm, c = 2625.2(6) pm, wR2 = 0.0373, 1378 F-2 values, 62 variables. The structure of YbPtSn contai ns two crystallographically different platinum positions. Both of them have tricapped trigonal prismatic coordination: [Pt1Sn(6)Yb(3)] and [Pt2Sn3Yb6] . Yb2Pt3Sn5 shows a close relation to the Y2Rh3Sn5 structure (space group C mc2(1)), however, with a different ordering of the platinum and tin atoms. Both ytterbium positions in Yb2Pt3Sn5 have the high coordination numbers (C N) of 20 for Yb1 and 18 for Yb2. Magnetic susceptibility measurements of Yb 2Pt3Sn5 show Curie-Weiss behavior between 50 K and room temperature with an experimental magnetic moment of mu(exp) = 2.6(1) mu(B)/Yb, indicating mixe d valency for the ytterbium atoms. Yb2Pt3Sn5 is a metallic conductor. Sn-11 9 Mossbauer spectroscopic data show one signal at delta = 1.75(1) mm/s for YbPtSn and delta = 2.02(1) mm/s for Yb2Pt3Sn5. Both spectra are subjected t o quadrupole splitting of Delta E-q = 0.59(5) mm/s (YbPtSn) and Delta E-q = 0.80(2) mm/s (Yb2Pt3Sn5).