“114”‐Type Nitrides LnAl(Si4−xAlx)N7Oδ with Unusual [AlN6] Octahedral Coordination

• Published in: Angewandte Chemie International Edition 2017-03, Vol.56 (14), p.3886-3891
• Main Authors: Huang, Saifang, Huang, Zhaohui, Cao, Peng, Zujovic, Zoran, Price, Jason R., Avdeev, Maxim, Que, Meidan, Suzuki, Furitsu, Kido, Tsuyoshi, Ouyang, Xin, Kaji, Hironori, Fang, Minghao, Liu, Yan‐gai, Gao, Wei, Söhnel, Tilo
• Format: Article
• Language: English
• Subjects: [AlN6] octahedron; aluminum; nitrides; NMR spectroscopy; structure elucidation
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201612488

Aluminum–nitrogen six‐fold octahedral coordination, [AlN6], 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(Si4−xAlx)N7Oδ (Ln=La, Sm), the first inorganic compounds with [AlN6] 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 P63mc symmetry where Ln and Al atoms locate in anticuboctahedral and octahedral interstitials, respectively, between the triangular and Kagomé layers of [SiN4] tetrahedra. Solid‐state NMR data of high‐purity La‐114 powders confirm the unusual [AlN6] 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. Six Ns and an Al: An extremely unusual coordination, [AlN6], is found in the La‐114 compound LnAl(Si4−xAlx)N7Oδ (Ln=La, Sm) prepared at normal pressure. The crystal structure confirms the existence of the octahedral coordination, as does 27Al NMR spectroscopy using La‐114 powders, giving a chemical shift of δ=3.5 ppm. The extra oxygen atoms distribute in a disordered manner surrounding [AlN6] octahedra.