BaSm5[Si9Al3N20]O – a nitridoaluminosilicate oxide with a new structure type composed of “star-shaped” [N[4]((Si,Al)N3)4] units as secondary building units

The nitridoaluminosilicate oxide BaSm5[Si9Al3N20]O was obtained by the reaction of barium and samarium metal, BaCO3, AlN and “Si(NH)2” in a radiofrequency furnace at temperatures around 1850 °C. The crystal structure was determined by single-crystal X-ray diffraction at 200(2) K (P  321, no. 150, Z=1Z=1, a=9.5101(8) Åa=9.5101(8) Å, c=6.1207(5) Åc=6.1207(5) Å, R1=0.0247R1=0.0247). It represents a new structure type with channels filled with chains of oxygen anions with corner sharing trigonal-bipyramidal coordination spheres. The anionic (Si,Al)/N 3D-network is made up solely of “star-shaped” [N[4]((Si,Al)N3)4] units consisting of four (Si,Al)N4 tetrahedra sharing a common central nitrogen atom. The structure refinement was performed utilizing an O/N-distribution model according to Paulings rules, i.e., nitrogen was positioned on all bridging sites and oxygen was positioned on the isolated position, resulting in charge neutrality of the compound. Thus a structure model representing a nitridoaluminosilicate oxide has been established. The Si and Al atoms have been distributed equally on their crystallographic sites, referring to their elemental proportion in the compound, due to being poorly distinguishable by X-ray methods. The chemical composition of the compound was derived from electron probe micro analyses (EPMA).

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