Structure and Properties of the Stannide Eu₂Au₂Sn₅, and its Relationship with the Family of BaAl₄-Related Structures

Abstract

The stannide Eu 2 Au 2 Sn 5 was prepared by high-frequency melting of the elements in a sealed tantalum tube. The structure of Eu 2 Au 2 Sn 5 was refined from single crystal X-ray data: P2 1 /m, a = 928.6(2), b = 465.8(2), c = 1042.9(3) pm, ß = 92.28(2)°, wR2 = 0.0653, 1220 F 2 values and 56 variables. The structure of Eu 2 Au 2 Sn 5 is of a new type, it can be considered as an ordered defect variant of the BaAl 4 type. Due to the ordered defects, the coordination number (CN) of the two crystallographically different europium sites is reduced from CN 16 to CN 14. The gold and tin atoms in Eu 2 Au 2 Sn 5 form a complex three-dimensional [Au 2 Sn 5 ] polyanion in which the europium atoms are embedded. Within the polyanion short Au-Sn and Sn-Sn distances are indicative of strongly bonding Au-Sn and Sn-Sn interactions. A detailed group-subgroup scheme for various ordered and defect variants of the BaAl 4 family is presented. Eu 2 Au 2 Sn 5 shows Curie-Weiss behavior above 50 K with an experimental magnetic moment of 7.90(5) μ B /Eu, indicating divalent europium. Antiferromagnetic ordering is detected at 5.8(5) K at low fields and a metamagnetic transition occurs at a critical field of 1.4(2) T. Eu 2 Au 2 Sn 5 is a metal with a specific resistivity of 150±20 μfΩcm at room temperature. The results of 151 Eu and 119 Sn Mössbauer spectroscopic experiments are compatible with divalent europium and show complex hyperfine field splitting with a transferred magnetic hyperfine field at the tin nuclei at low temperature.