NaAuSe - A selenoaurate with cyclic anions

Transparent deep orange crystals of NaAuSe were obtained by fusing together stoichiometric amounts of Na2Se, Au and Se at 730 degrees C, followed by slow cooling of the melt. NaAuSe is tetragonal, tI48, space group I4(1)/amd (No. 141), Z = 16 with a = 9.772(2) Angstrom, c = 11.469(2) Angstrom. The crystal structure was determined from single crystal diffractometer data and refined to a conventional R of 0.030 (276 F-o values, 20 variables). An outstanding feature of the crystal structure is the formation of discrete anions, which consist of V-shaped eight-membered rings, [Au4Se4](4-). Au is in an almost linear coordination by Se (angle Se-Au-Se: 168.31 degrees, d(Au-Se): 2.457(2) Angstrom); the bond angle on Se is only 82.9(1)degrees. The crystal structure is based on a c.c.p.-packing of the chalcogen atoms.