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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.

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

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.

Keywords: high pressure; π‐stacking; organic radicals; intermolecular interactions; phase transitions

The intramolecular conformational response to the build‐up of compressed intermolecular interactions in Blatter's radical (1,3‐diphenyl‐1,4‐dihydrobenzo[e][1,2,4]triazin‐4‐yl) induces a second‐order premonitory phase transition and then a first‐order phase transition above 5.34 GPa.

The full text for this article, hosted at journals.iucr.org, is unavailable due to technical difficulties.

Supporting information for this article can be found http://scripts.iucr.org/cgi-bin/paper?um5054

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

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Titel:	A first-order phase transition in Blatter's radical at high pressure.
Autor/in / Beteiligte Person:	Broadhurst, ET ; Wilson, CJG ; Zissimou, GA ; Nudelman, F ; Constantinides, CP ; Koutentis, PA ; Parsons, S
Link:	Volltext (PDF)
Zeitschrift:	Acta crystallographica Section B, Structural science, Jg. 78 (2022-04-01), Heft Pt 2, S. 107-116
Veröffentlichung:	Oxford : Wiley-Blackwell, 2013-, 2022
Medientyp:	academicJournal
ISSN:	2052-5206 (electronic)
DOI:	10.1107/S2052520622000191
Schlagwort:	Crystallography, X-Ray Density Functional Theory Dimerization Molecular Conformation Pressure Triazines chemistry Phase Transition
Sonstiges:	Nachgewiesen in: MEDLINE Sprachen: English Publication Type: Journal Article Language: English [Acta Crystallogr B Struct Sci Cryst Eng Mater] 2022 Apr 01; Vol. 78 (Pt 2), pp. 107-116. <i>Date of Electronic Publication: </i>2022 Feb 16. MeSH Terms: Phase Transition* ; Crystallography, X-Ray ; Density Functional Theory ; Dimerization ; Molecular Conformation ; Pressure ; Triazines / chemistry Grant Information: EP-M506515-1 Engineering and Physical Sciences Research Council; EP/R042845/1 Engineering and Physical Sciences Research Council Contributed Indexing: Keywords: high pressure; intermolecular interactions; organic radicals; phase transitions; π-stacking Substance Nomenclature: 0 (Triazines) Entry Date(s): Date Created: 20220412 Date Completed: 20220413 Latest Revision: 20220531 Update Code: 20231215

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