"114"-Type Nitrides LnAl(Si sub(4-x)Al sub(x))N sub(7)O sub( delta ) with Unusual [AlN sub(6)] Octahedral Coordination

Aluminum-nitrogen six-fold octahedral coordination, [AlN sub(6)], is unusual and has only been seen in the high-pressure rocksalt-type aluminum nitride or some complex compounds. Herein we report novel nitrides LnAl(Si sub(4-x)Al sub(x))N sub(7)O sub( delta ) (Ln=La, Sm), the first inorganic compounds with [AlN sub(6)] coordination prepared via non-high-pressure synthesis. Structure refinements of neutron powder diffraction and single-crystal X-ray diffraction data show that these compounds crystallize in the hexagonal Swedenborgite structure type with P6 sub(3)mc symmetry where Ln and Al atoms locate in anticuboctahedral and octahedral interstitials, respectively, between the triangular and Kagome layers of [SiN sub(4)] tetrahedra. Solid-state NMR data of high-purity La-114 powders confirm the unusual [AlN sub(6)] coordination. These compounds are the first examples of the "33-114" sub-type in the "114" family. The additional site for over-stoichiometric oxygen in the structure of 114-type compounds was also identified.Original Abstract: 6 N, 1 Al: Das unuebliche [AlN sub(6)]-Koordinationsmuster findet sich bei der bei Normaldruck hergestellten La-114-Verbindung LnAl(Si sub(4-x)Al sub(x))N sub(7)O sub([delta]) (Ln=La, Sm). Eine Kristallstrukturanalyse bestaetigt diese Oktaederkoordination, ebenso wie die chemische Verschiebung von [delta]=3.5ppm in super(27)Al-NMR-Spektren von La-114-Pulvern. Die zusaetzlichen Sauerstoffatome umgeben die [AlN sub(6)]-Oktaeder in ungeordneter Weise.