A high-pressure single-crystal X-ray diffraction study of potassium guaninate hydrate, K⁺?C₅H₄N₅O^-?H₂O

The crystal structure of potassium guaninate hydrate, K+center dot C5H4N5O-center dot H2O, was studied in the pressure range of 1 atm to 7.3 GPa by single-crystal diffraction using synchrotron radiation and a laboratory X-ray diffraction source. Structural strain was compared to that of the same salt hydrate on cooling, and in 2Na(+)center dot C5H3N5O2-center dot 7H(2)O under hydrostatic compression and on cooling. A polymorphic transition into a new, incommensurately modulated, phase was observed at similar to 4-5 GPa. The transition was reversible with a hysteresis: the satellite reflections disappeared on decompression to similar to 1.4 GPa.