THE CRYSTAL-STRUCTURE OF AUNI2SN4

A hitherto unknown, virtually stoichiometric phase with composition Au Ni2Sn4 has been identified in the Au-Ni-Sn system, and its structure h as been determined by direct methods. The unit cell is rhombohedral (s pace group: R(3) over barm$) with dimensions a = 422.6(1) pm and c = 2 656.6(4) pm in the hexagonal setting and a = 918.2(2) pm and alpha = 2 6.60(1)degrees in the rhombohedral setting. According to the hexagonal description Au is in 3b and Ni, Sn(I), and Sn(II) are in 6c with z = 0.40091(6), 029965(3), and 0.11204(3), respectively. AuNi2Sn4 proves t o be isostructural with the mineral smythite (Fe3S4-s). The Fe3S4-s-ty pe structure belongs to the NiAs-type family and certain aspects of th e structural relationships are briefly discussed. (C) 1995 Academic Pr ess,Inc.