Pentacoordinate phosphorus in a high-pressure polymorph of phosphorus nitride imide P4N6(NH).

Coordination numbers higher than usual are often associated with superior mechanical properties. In this contribution we report on the synthesis of the high-pressure polymorph of highly condensed phosphorus nitride imide P4 N6 (NH) representing a new framework topology. This is the first example of phosphorus in trigonal-bipyramidal coordination being observed in an inorganic network structure. We were able to obtain single crystals and bulk samples of the compound employing the multi-anvil technique. γ-P4 N6 (NH) has been thoroughly characterized using X-ray diffraction, solid-state NMR and FTIR spectroscopy. The synthesis of γ-P4 N6 (NH) gives new insights into the coordination chemistry of phosphorus at high pressures. The synthesis of further high-pressure phases with higher coordination numbers exhibiting intriguing physical properties seems within reach.