Pressure-induced isosymmetric phase transition in biurea. Issue 39 (9th September 2019)

• Record Type: Journal Article
• Authors: Bull, Craig L.; Funnell, Nicholas P.; Ridley, Christopher J.; Pulham, Colin R.; Coster, Paul L.; Tellam, James P.; Marshall, William G.
• Is Part Of: CrystEngComm. Volume 21:Issue 39(2019)
• Page Start: 5872
• Page End: 5881
• Publication Date: 2019-09-09
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/c9ce01028a
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : An isosymmetric phase transition of biurea has been found in which the molecules appear to "snap" from one conformer to another upon compression. Abstract : We report a pressure-induced transition to a new crystalline phase of biurea (C2 D6 N4 O2 ). Neutron-powder diffraction and Raman spectra, measured up to 3.89 GPa reveal this transition to be isosymmetric, where substantial intramolecular reorientation leads to an abrupt decrease in unit cell volume at ∼0.6 GPa and an increase in some intermolecular contact distances. DFT and vibrational energy calculations suggest that the ambient pressure phase is stabilised by zero point energy and entropy, until the pressure–volume–driven transition at 0.6 GPa.