PREPARATION AND CRYSTAL-STRUCTURE OF A NEW BARIUM SILICON-NITRIDE, BA5SI2N6

Single crystals of a new ternary nitride, Ba5Si2N6, were synthesized b y slow cooling from 750 degrees C using a starting mixture of Ba, Si, Na and NaN3, where Na and NaN3 were a flux and a nitrogen source respe ctively. It crystallizes with orthorhombic symmetry: space group P2(1) 2(1)2(1) (No. 19), a = 6.159, b = 10.305, c = 15.292 Angstrom, and Z = 4. The crystal structure was determined from single-crystal data and refined to R1 = 0.0495 for all 1637 observed reflections and 89 variab les. A pair of SiN4 tetrahedra contained in the structure forms a nitr idometallate anion of [Si2N6](10-) by edge sharing.