Mixed Tin Valence in the Tin(II/IV)-Nitridophosphate Sn3P8N16.

Sn3P8N16 combines the structural versatility of nitridophosphates and Sn within one compound. It was synthesized as dark gray powder in a high-pressure high-temperature reaction at 800 °C and 6 GPa from Sn3N4 and P3N5. The crystal structure was elucidated from single-crystal diffraction data (space group C2/m (no. 12), a=12.9664(4), b=10.7886(4), c=4.8238(2) Å, ß=109.624(1)°) and shows a 3D-network of PN4 tetrahedra, incorporating Sn in oxidation states +II and +IV. The Sn cations are located within eight-membered rings of vertex-sharing PN4 tetrahedra, stacked along the [001] direction. A combination of solid-state nuclear magnetic resonance spectroscopy, 119Sn Mössbauer spectroscopy and density functional theory calculations was used to confirm the mixed oxidation of Sn. Temperature-dependent powder X-ray diffraction measurements reveal a low thermal expansion of 3.6 ppm/K up to 750 °C, beyond which Sn3P8N16 starts to decompose.

Finding Order in Disorder: The Highly Disordered Lithium Oxonitridophosphate Double Salt Li8+x P3 O10-x N1+x (x=1.4(5)).

The crystalline lithium oxonitridophosphate Li8+x P3 O10-x N1+x , was obtained in an ampoule synthesis from P3 N5 and Li2 O. The compound crystallizes in the triclinic space group P 1 - ${\mathrel{\mathop{{\rm { 1}}}\limits^{{\rm -}}}}$ with a=5.125(2), b=9.888(5), c=10.217(5) Å, α=70.30(2), ß=76.65(2), γ=77.89(2)°. Li8+x P3 O10-x N1+x is a double salt, the structure of which contains distinctive complex anion species, namely non-condensed P(O,N)4 tetrahedra, and P(O,N)7 double tetrahedra connected by one N atom. Additionally, there is mixed occupation of O/N positions, which enables further anionic species by variation of O/N occupancies. To characterize these motifs in detail, complementary analytical methods were applied. The double tetrahedron exhibits significant disorder in single-crystal X-ray diffraction. Furthermore, the title compound is a Li+ ion conductor with a total ionic conductivity of 1.2×10-7  S cm-1 at 25 °C, and a corresponding total activation energy of 0.47(2) eV.