Structure and properties of Eu2Pt3Sn5

The new stannide Eu2Pt3Sn5 was synthesized by induction melting of the elements in a sealed tantalum tube in a water-cooled silica sample chamber. The structure was refined on the basis of single crystal X-ray diffractometer data: Y2Rh3Sn5 type, Cmc2(1), a = 453.30(9), b = 2662.9(8), c = 731.8(2) pm, wR(2) = 0.0472, 1493 F-2 values and 62 variables). The platinum and tin atoms build up a complex three-dimensional [Pt3Sn5] network with a broad range of Pt-Sn (264-293 pm) and Sn-Sn (308-373 pm) distances. The two crystallographically independent europium sites occupy large voids of coordination numbers 20 (Eu1) and 18 (Eu2) within the [Pt3Sn5] network. Eu2Pt3Sn5 shows Curie-Weiss behaviour in the temperature range 50-305 K with an experimental magnetic moment of 7.82(1) mu(B) per Eu atom indicating purely divalent europium. C-p, measurements show a broad anomaly with two maxima at 4.9(2) and 6.1(2) K. Eu-151 Mossbauer spectra revealed both crystallographically independent europium sites to be divalent. At 4.2 K two rather different sizes of magnetic hyperfine field splittings are observed due to separate ordering of the two sites. The Sn-119 Mossbauer spectrum shows complex superposition of the five signals in the paramagnetic range.