Pressure-induced collapse of guanidinium nitrate N–H⋯O bonded honeycomb layers into a 3-D pattern with varied H-acceptor capacity

Highly favoured N-H···O bonded honeycomb layers in guanidinium nitrate, C(NH(2))(3)(+)NO(3)(-), have been destabilized by a pressure of 0.6 GPa, and the novel motif of 3-dimensional N-H···O bonded aggregation in high-pressure phase IV determined for in situ grown single-crystal by X-ray diffraction. The mechanism of the transition involves the collapse of voids present in phases I, II and III. In the P/T phase diagram a large hysteresis of the phase IV boundaries is caused by the strongly reconstructive character of the transition and pressure dependent H-accepting capacity of oxygen atoms.