Structure of Tetrakis(melaminium) Bis(dihydrogenphosphate) Monohydrogenphosphate Trihydrate from X-ray Powder Diffraction and Solid-State NMR Spectroscopy

The crystal structure of the melamine phosphate salt tetrakis(melaminium) bis(dihydrogenphosphate) monohydrogenphosphate trihydrate with as much as ten independent moieties in the unit cell was determined by a direct-space global optimization technique from X-ray powder diffraction data using additional geometry constraints obtained by ³¹P double-quantum solid-state NMR spectroscopy. The structure analysis of the compound and its comparison with other melamine phosphates reveals the packing and bonding characteristics that are important for melamine-phosphate salts with a melamine-to-phosphor ratio larger than one, which are promising environmental-friendly flame retardants.