Synthesis, crystal structure, and properties of a new sialon -: SrSiAl2O3N2

The sialon SrSiAl2O3N2 was obtained as a coarsly crystalline solid by reaction of silicon diimide, aluminum nitride, and strontium carbonate under N-2 atmosphere in a high-frequency furnace at 1650 degrees C. According to the single-crystal structure determination the title compound is isotypic with LnSi(3)N(5) (Ln = La, Ce, Nd, Pr). SrSiAl2O3N2 (P2(1)2(1)2(1), a = 491.98(6), b = 789.73(7), c = 1134.94(18) pm, Z = 4, R1 = 0.0439, wR2 = 0.0939). In the solid a three-dimensional network structure of corner sharing SiON3, AlO3N, and AlO2N2 tetrahedra occurs. Lattice energetic calculations using the MAPLE concept confirm an unequivocally correct crystallographic differentiation between N and O as well as Al and Si atoms, respectively (Al-O: 167.4(5)-170.6(6); Al-N: 175.4(6)-179.4(6); Si-O: 171.2(6); SiN: 176.7(6)-179.6(6) pm). The Sr2+ ions are located in the voids of the (SiAl2O3N2)(2-) framework (Sr-O: 250.4(6)-304.2(6); Sr-N: 287.4(6) 318.2(6) pm).