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

Sn 3 P 8 N 16 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 Sn 3 N 4 and P 3 N 5 . The crystal structure was elucidated from single‐crystal diffraction data (space group C 2/ m (no. 12), a =12.9664(4), b =10.7886(4), c =4.8238(2) Å, β =109.624(1)°) and shows a 3D‐network of PN 4 tetrahedra, incorporating Sn in oxidation states +II and +IV. The Sn cations are located within eight‐membered rings of vertex‐sharing PN 4 tetrahedra, stacked along the [001] direction. A combination of solid‐state nuclear magnetic resonance spectroscopy, 119 Sn 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 Sn 3 P 8 N 16 starts to decompose.