A first-order phase transition in Blatter's radical at high pressure

Edward T. Broadhurst, Cameron J. G. Wilson, Georgia A. Zissimou, Fabio Nudelman, Christos P. Constantinides, Panayiotis A. Koutentis, Simon Parsons

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

The crystal structure of Blatter's radical (1,3-di­phenyl-1,4-di­hydro­benzo[e][1,2,4]triazin-4-yl) has been investigated between ambient pressure and 6.07 GPa. The sample remains in a compressed form of the ambient-pressure phase up to 5.34 GPa, the largest direction of strain being parallel to the direction of π-stacking interactions. The bulk modulus is 7.4 (6) GPa, with a pressure derivative equal to 9.33 (11). As pressure increases, the phenyl groups attached to the N1 and C3 positions of the triazinyl moieties of neighbouring pairs of molecules approach each other, causing the former to begin to rotate between 3.42 to 5.34 GPa. The onset of this phenyl rotation may be interpreted as a second-order phase transition which introduces a new mode for accommodating pressure. It is premonitory to a first-order isosymmetric phase transition which occurs on increasing pressure from 5.34 to 5.54 GPa. Although the phase transition is driven by volume minimization, rather than relief of unfavourable contacts, it is accompanied by a sharp jump in the orientation of the rotation angle of the phenyl group. DFT calculations suggest that the adoption of a more planar conformation by the triazinyl moiety at the phase transition can be attributed to relief of intramolecular H⋯H contacts at the transition. Although no dimerization of the radicals occurs, the π-stacking interactions are compressed by 0.341 (3) Å between ambient pressure and 6.07 GPa.
Original languageEnglish
JournalActa Crystallographica Section B Structural Science, Crystal Engineering and Materials
Issue number2
Early online date16 Feb 2022
Publication statusE-pub ahead of print - 16 Feb 2022


Dive into the research topics of 'A first-order phase transition in Blatter's radical at high pressure'. Together they form a unique fingerprint.

Cite this