Secondary Au-Au and Sn-Sn interactions in the superstructure of YbAuSn-missing link in the series of KHg2 superstructures

The stannide YbAuSn has been synthesized in quantitative yield by reacting the elements in sealed tantalum tubes in a high-frequency furnace. The structure was determined from single-crystal X-ray data: Imm2, a = 469.7(1) pm, b = 2191.2(4) pm, c = 812.7(1) pm, wR2 = 0.111, 2061 F-2 values, and 58 variables. It crystallizes with a pronounced KHg2 type subcell (a, 1/3b, c, Imma). In the superstructure the tripled b axis allows an ordered stacking of Au3Sn3 hexagons with weak gold-tin, gold-gold, and tin-tin interlayer bonding interactions. The determined stacking sequence - + - - + -, - + - - + - in YbAuSn realizes a so far missing sequence within a general ordering scheme of KHg2 type superstructures. The group-subgroup relation in going from the KHg2 subcell and chemical bonding in YbAuSn are discussed. Each ytterbium site has an ordered near-neighbor environment of six gold and six tin atoms in the form of two tilted hexagons. Magnetic susceptibility measurements show a nonmagnetic ground state of the ytterbium atoms. YbAuSn is a metallic conductor with a specific resistivity of 50 mu Omega cm at room temperature. Sn-119 Mossbauer spectroscopic data show one signal at an isomer shift of 1.922(5) mm/s subjected to quadrupole splitting of 0.929(9) mm/s.