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 °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 F d d d (No. 70-2), a = 7.9095(3) Å, b = 11.2972(5) Å, c = 20.4009(12) Å, 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) Å, b = 6.7868(3) Å, c = 13.3249(5) Å, β = 101.7070(13)°) and Ba1.6Sr3.4[Si2N6] (a = 10.2406(5) Å, b = 6.6715(3) Å, c = 13.5166(8) Å, β = 100.274(2)°) are isotypic with Ca5[Si2N6].

A novel nitride, Ba4Mg[Si2N6], containing [Si2N6]10− double tetrahedra, was prepared using a Na flux. Mg atoms are at planar rectangular nitrogen coordination sites.Figure optionsDownload as PowerPoint slideHighlights
► Novel nitrides, Ba4Mg[Si2N6], Ba3Ca2[Si2N6], Ba1.6Sr3.4[Si2N6], were found.
► Single crystals of the quaternary nitrides were synthesized by the Na flux method.
► The quaternary nitrides were composed of [Si2N6]10− double tetrahedra.
► Ba3Ca2[Si2N6] and Ba1.6Sr3.4[Si2N6], are isotypic with Ca5[Si2N6].
► Mg2− cations are at a planar–rectangular nitrogen coordination site in Ba4Mg[Si2N6].