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Synthesis and Crystal Structures of Ca4SiN4 and New Polymorph of Ca5Si2N6

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posted on 06.05.2013, 00:00 by Hisanori Yamane, Haruhiko Morito
Single crystals of Ca4SiN4 were found in the product prepared by heating Ba, Ca, Si, NaN3, and Na at 900 °C. Ca4SiN4 [space group P21/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 Ca2+ and edge-sharing double tetrahedra [Si2N6]10–.