Ba4Mg[Si2N6], Ba3Ca2[Si2N6] and Ba1.6Sr3.4[Si2N6] - Quaternary barium alkaline-earth silicon nitrides containing isolated nitridosilicate anions of [Si2N6]10-

Ba4Mg[Si2N6], Ba3Ca2[Si2N6], and Ba1.6Sr3.4[Si2N6] were synthesized by heating Ba, AE (=Mg, Ca, and Sr), Si, NaN3 and Na at 900 degrees C. The crystal structures of these compounds consist of alkaline-earth metal cations and edge-sharing SiN4 tetrahedra of isolated nitridosilicate anions [Si2N6](10-). Ba4Mg[Si2N6] crystallizes in a new orthorhombic structure type, space group Fddd (No. 70-2), a = 7.9095(3) angstrom, b = 11.2972(5) angstrom, c = 20.4009(12) angstrom, and Z = 8. Mg2+ cations are planar-rectangularly coordinated by four nitrogen atoms. The monoclinic crystal structures (C2/c (No. 15), Z = 4) of Ba3Ca2[Si2N6] (a = 10.0962(4) angstrom, b = 6.7868(3) angstrom, c = 13.3249(5) angstrom, beta = 101.7070(13)degrees) and Ba1.6Sr3.4[Si2N6] (a = 10.2406(5) angstrom, b = 6.6715(3) angstrom, c = 13.5166(8) angstrom, beta = 100.274(2)degrees) are isotypic with Ca-5[Si2N6]. (C) 2012 Elsevier B.V. All rights reserved.