Pressure-induced phase transition in guanidinium perchlorate: a supramolecular structure directed by hydrogen bonding and electrostatic interactions.

In situ Raman spectroscopy and synchrotron X-ray diffraction (XRD) experiments have been performed to investigate the response of guanidinium perchlorate (C(NH(2))(3)(+)·ClO(4)(-), GP) to high pressures of ∼11 GPa. GP exhibits a typical supramolecular structure of two-dimensional (2D) hydrogen-bonded ionic networks at ambient conditions. A subtle phase transition, accompanied by the symmetry transformation from R3m to C2, has been confirmed by obvious changes in both Raman and XRD patterns at 4.5 GPa. The phase transition is attributed to the competition between hydrogen bonds and close packing of the supramolecular structure at high pressure. Hydrogen bonds have been demonstrated to evolve into a distorted state through the phase transition, accompanied by the reduction in separation of oppositely charged ions in adjacent sheet motifs. A detailed mechanism of the phase transition, as well as the cooperativity between hydrogen bonding and electrostatic interactions, is discussed by virtue of the local nature of the structure.