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

The crystal structure of potassium guaninate hydrate, K⁺·C₅H₄N₅O^-·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⁺·C₅H₃N₅O^2-·7H₂O under hydrostatic compression and on cooling. A polymorphic transition into a new, incommensurately modulated, phase was observed at ∼4-5 GPa. The transition was reversible with a hysteresis: the satellite reflections disappeared on decompression to ∼1.4 GPa.