Synthesis, Crystal and Electronic Structure of the Nitridoaluminosilicate Ca5[Si2Al2N8]

Ca-5[Si2Al2N8] was synthesized from elementary aluminum and silicon with phase-pure tricalcium dinitride at 1280 K under dry argon in a sealed niobium ampoule. Ca3N2 was freshly prepared from distilled calcium metal in a dry nitrogen atmosphere. The compound crystallizes in form of transparent yellow distorted octahedra. In air and under moisture Ca-5[Si2Al2N8] undergoes hydrolysis. The structure was determined from a single crystal to be orthorhombic (space group Pbcn - no. 60, a = 925.5, b = 614.0 and c = 1557.8 pm). The nitridoaluminate and -silicate substructures are separated into planes of edge and corner-shared aluminate tetrahedra, which are linked by edge-sharing double tetrahedral pillars of the silicate. The structure was confirmed by electrostatic and quantum mechanical analysis.