Na5AuSe12-the first selenoaurate(III) with discrete complex anions

The novel polyselenoaurate(III) Na5AuSe12 was prepared by reacting a stoichiometric mixture of Na2Se, Au and Se at 345?C followed by slow cooling. Na5AuSe12 forms transparent red crystals of lamellar habit. It is monoclinic, mP36, s.g. P21, with a=7.145(1)Ä, b=16.790(6)Ä, c=8.291(1)Ä, ß=107.13(1)?, Z=2. The crystal structure was determined from diffractometer data and refined to a conventional R of 0.032 (3830 Fo's, 163 variables). Na5AuSe12 contains discrete mononuclear anions [AuSe12](5-) which are formed by four triselenide chains in end-on coordination with the central atom. The Au-atom is in an almost undistorted square planar coordination through Se. The mean Au-Se bond length is 2.500Ä, Se-Se bond lengths in the Se3-chains are in the range of 2.346-2.363Ä. The shortest intra-anionic Se-Se-contacts are in the range of 3.19-3.27Ä. In the crystal structure the [AuSe12](5-) anions are stacked in columns along [100]. Together with three of the five crystallographically independent Na(+)-ions the columns are arranged in slabs parallel to (010)-plane which are separated by layers of the remaining Na(+)-ions. Na5AuSe12 is the first alkali selenoaurate(III) containing molecular anions. It undergoes peritectic decomposition at 275?C and is soluble in dimethylformamide.