Multicationic Tetrahedra Networks: Alkaline-Earth-Centered Polyhedra and Non-Condensed AlN-Octahedra in the Imidonitridophosphates AEAlPN(NH) (AE=Ca, Sr, Ba).

A series of isostructural imidonitridophosphates AEAlPN(NH) (AE=Ca, Sr, Ba) was synthesized at high-pressure/high-temperature conditions (1400 °C and 5-9 GPa) from alkaline-earth metal nitrides or azides CaN/Sr(N)/Ba(N) and the binary nitrides AlN and PN. NHF served as a hydrogen source and mineralizing agent. The crystal structures were determined by single-crystal X-ray diffraction and feature a three-dimensional network of vertex-sharing PN-tetrahedra forming diverse-sized rings that are occupied by aluminum and alkaline earth ions. These structures represent another example of nitridophosphate-based networks that simultaneously incorporate AlN-octahedra and alkaline-earth-centered polyhedra, with aluminum not participating in the tetrahedra network. They differ from previously reported ones by incorporating non-condensed octahedra instead of strongly condensed octahedra units and contribute to the diversity of multicationic nitridophosphate network structures. The results are supported by atomic resolution EDX mapping, solid-state NMR and FTIR measurements. Eu-doped samples show strong luminescence with narrow emissions in the range of green to blue under UV excitation, marking another instance of Eu-luminescence within imidonitridophosphates.