SrP3N5O: A Highly Condensed Layer Phosphate Structure Solved from a Nanocrystal by Automated Electron Diffraction Tomography

The oxonitridophosphate SrP3N5O has been synthesized by heating a multicomponent reactant mixture that consisted of phosphoryl triamide OP(NH2)(3), thiophosphoryl triamide SP(NH2)(3), SrS, and NH4Cl enclosed in evacuated and sealed silica-glass ampoules up to 750 degrees C. The compound was obtained as nanocrystalline powder with needle-shaped crystallites. The crystal structure was solved ab initio on the basis of electron diffraction data by means of automated electron diffraction tomography (ADT) and verified by Rietveld refinement with X-ray powder diffraction data. SrP3N5O crystallizes in the orthorhombic space group Pnma (no. 62) with unit-cell data of a = 18.331(2), b = 8.086(1), c = 13.851(1) angstrom and Z = 16. The compound is a highly condensed layer phosphate with a degree of condensation kappa = 1/2. The corrugated layers (2)(infinity){(P3N5O)(2-)} consist of linked, triangular columns built up from P(O, N)(4) tetrahedra with 3-rings and triply binding nitrogen atoms. The Sr2+ ions are located between the layers and exhibit six-, eight-, and ninefold coordination. FTIR and solid-state NMR spectra of SrP3N5O are discussed as well.