High-pressure synthesis and structural investigation of H3P8O8N9: a new phosphorus(V) oxonitride imide with an interrupted framework structure.

The first crystalline phosphorus oxonitride imide H(3)P(8)O(8)N(9) (=P(8)O(8)N(6)(NH)(3)) has been synthesized under high-pressure and high-temperature conditions. To this end, a new, highly reactive phosphorus oxonitride imide precursor compound was prepared and treated at 12 GPa and 750 °C by using a multianvil assembly. H(3)P(8)O(8)N(9) was obtained as a colorless, microcrystalline solid. The crystal structure of H(3)P(8)O(8)N(9) was solved ab initio by powder X-ray diffraction analysis, applying the charge-flipping algorithm, and refined by the Rietveld method (C2/c (no. 15), a=1352.11(7), b=479.83(3), c=1820.42(9) pm, β=96.955(4)°, Z=4). H(3)P(8)O(8)N(9) exhibits a highly condensed (κ=0.47), 3D, but interrupted network that is composed of all-side vertex-sharing (Q(4)) and only threefold-linking (Q(3)) P(O,N)(4) tetrahedra in a Q(4)/Q(3) ratio of 3:1. The structure, which includes 4-ring assemblies as the smallest ring size, can be subdivided into alternating open-branched zweier double layers {oB,2(2)(∞)}[(2)P(3)(O,N)(7)] and layers containing pairwise-linked Q(3) tetrahedra parallel (001). Information on the hydrogen atoms in H(3)P(8)O(8)N(9) was obtained by 1D (1)H MAS, 2D homo- and heteronuclear (together with (31)P) correlation NMR spectroscopy, and a (1)H spin-diffusion experiment with a hard-pulse sequence designed for selective excitation of a single peak. Two hydrogen sites with a multiplicity ratio of 2:1 were identified and thus the formula of H(3)P(8)O(8)N(9) was unambiguously determined. The protons were assigned to Wyckoff positions 8f and 4e, the latter located within the Q(3) tetrahedra layers.