High-Pressure-Induced Phase Transitions in Pentaerythritol:  X-ray and Raman Studies

Abstract

The high-pressure response of pentaerythritol crystals has been examined to 10 GPa in diamond-anvil cells using angle-dispersive synchrotron X-ray diffraction and Raman spectroscopy. The results reveal two first-order phase transitions: one at 4.8 GPa from phase I, tetragonal I(), to phase II, orthorhombic Pnn2C2v10, with a small approximately 0.5% volume change, and the other at 7.2 GPa to phase III with an unknown crystal structure. We found that phase I exhibits a large crystallographic anisotropy which rapidly decreases with increasing pressure: the ratio of linear compressibilities between two primary crystal axes decreases from betao= 8.1 at 1 atm to betaP = 2.6 at 4 GPa. We suggest that this apparent decrease in crystal anisotropy is due to the disruption of hydrogen bonding in the (001) plane of phase I and eventually leads to an orthorhombic distortion from a quadrilateral network structure in phase I to a quasi one-dimensional structure in phase II. The crystal structure of phase III exhibits a disordered character, and it is likely a conformational variant of phase II.

Structural Properties and Halogen Bonds of Cyanuric Chloride under High Pressure

“…The best fits were found to be B 0 = 8.4 ± 0.5 GPa and B 0 ′ = 10.7 ± 0.4 GPa . As was observed for many other molecular crystals, − the compressibility was high and the compressional behavior of cyanuric chloride was anisotropic, with the c -axis being more compressible than the a - and b -axes. These compressional behaviors could be explained by taking into account the layered crystal packing.…”

Pressure-Induced Phase Transition in Guanidinium Perchlorate: A Supramolecular Structure Directed by Hydrogen Bonding and Electrostatic Interactions

“…When pressure is beyond 4.5 GPa, the bands reveal much faster blue shifts, as shown in Figure b. The variation in the pressure coefficients implies that the N–H···O hydrogen bonds may evolve into a distorted state at 4.5 GPa, similar to the evolution of hydrogen bonds in pentaerythritol . Nevertheless, the quasi 2D rosette hydrogen network is proposed to be preserved in phase II, since the four modes keep their initial distribution in position and intensity over 4.5 GPa.…”

“…The variation in the pressure coefficients implies that the NÀH 3 3 3 O hydrogen bonds may evolve into a distorted state at 4.5 GPa, similar to the evolution of hydrogen bonds in pentaerythritol. 39 Nevertheless, the quasi 2D rosette hydrogen network is proposed to be preserved in phase II, since the four modes keep their initial distribution in position and intensity over 4.5 GPa. Therefore, the subtle phase transition at 4.5 GPa is not associated with reconstruction of guanidinium cations and perchlorate anions.…”

Pressure-Induced Phase Transition in N–H···O Hydrogen-Bonded Molecular Crystal Oxamide

“…This accounts for the high compressibility of the a -axis. We conclude that oxamide has a high and anisotropic compressibility which is common in organic crystals. − Meanwhile, the cell volume reduces significantly at 9.7 GPa, indicating the crystal structure is more compact in phase II.…”