A quintupled superstructure of the KHg2 type realized for the new stannide EuAuSn

The title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K. EuAuSn crystallizes with a pronounced subcell of space group Imma (KHg2 type). Additional very weak reflections required a quintupled b axis. The superstructure was refined from single-crystal four-circle diffractometer data (Imm 2, a = 479.1 (1) pm, b = 3833.6(5) pm, c = 820.1(1) pm, Z = 20, wR2 = 0.0834, 3675F(2) values and 94 variables). Six crystallographically different europium sites occur in the superstructure. Each europium site has an ordered near-neighbour environment of six gold and six tin atoms in the form of two tilted hexagons. Magnetic susceptibility measurements show Curie-Weiss behaviour above 50 K with an experimental magnetic moment of 7.6(1) mu(B)/Eu, indicating divalent europium. EuAuSn orders antiferromagnetically at about 12 K and undergoes a metamagnetic transition at a critical field of 2.0(2) T. Electrical conductivity measurements show metallic behaviour with a room temperature value of 260 mu Omega cm. Eu-151 and Sn-119 Mossbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting at low temperature.