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

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(Si_4−x Al_x)N₇O_δ (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 P 6₃mc 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.