Modular Principle for Complex Disordered Tetrahedral Frameworks in Quenched High-Pressure Phases of Phosphorus Oxide Nitrides

Abstract

The crystal structures of the new phosphorus oxide nitrides P40O31N46 and P74O59N84, which were synthesized from amorphous phosphorus oxide nitride imide, exhibit complex frameworks built up from P(O,N)4 tetrahedra. The latter form various chain-like building units with various degrees of branching. These modular units can be combined and arranged in different ways, which leads to closely related structures and several disordered configurations in each compound. As the material was obtained by high-pressure high-temperature synthesis, the disorder is most likely a consequence of quenching a high-pressure phase with P(O,N)5 trigonal bipyramids. Under ambient conditions, P atoms are expected to relax by moving to the centers of the face-sharing tetrahedra that constitute the bipyramid. Diffraction patterns acquired with microfocused synchrotron radiation reveal that domains of both compounds are intergrown with H3P8O8N9, whose tetrahedral framework represents a cutout of the structures of both P40O31N46 and P74O59N84. Powder diffraction patterns do not indicate any further phases.