title: Synthesis and crystal structures of Ca4SiN4 and new polymorph of Ca5Si2N6.
abstract: Single crystals of Ca4SiN4 were found in the product prepared by heating Ba, Ca, Si, NaN3, and Na at 900 °C. Ca4SiN4 [space group P2(1)/c (No. 14), Z = 4, a = 9.1905(4) Å, b = 5.9775(3) Å, c = 11.0138(7) Å, β = 116.4054(17)°] is isotypic with Ca4GeN4 and K4SiO4. Isolated [SiN4](8-) tetrahedra were identified in the structure by single-crystal X-ray diffraction. After reheating the product at 900 °C, a new polymorph of Ca5Si2N6 crystallized. The space group of the polymorph [C2/m (No. 12), Z = 4, a = 6.2712(5) Å, b = 10.0175(8) Å, c = 12.0287(8) Å, β = 99.303(2)°] is different from C2/c previously reported for Ca5Si2N6, while both polymorphs are composed of Ca(2+) and edge-sharing double tetrahedra [Si2N6](10-).
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Aoba-ku, Sendai 980-8577, Japan. yamane@tagen.tohoku.ac.jp
authors.forename: Hisanori
authors.initials: H
authors.lastname: Yamane
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Morito