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Lookup NU author(s): Max Hill, Dr Jon Sellars, Alexandra Longcake, Dr Paul Waddell
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© 2026 The Authors. Published by American Chemical SocietyThe structures of 2-amino-4′-chlorobenzophenone and 2-amino-4′-bromobenzophenone, previously determined at room temperature in the space group Pna21, have been redetermined at low-temperature revealing two different reversible phase transitions. Additionally, high-pressure X-ray diffraction studies were conducted to allow for a comparison of the behavior of these structures in response to different external stimuli. Variable temperature analyses reveal that 2-amino-4′-bromobenzophenone transitions to the monoclinic space group Pa accompanied by a nonmerohedral twinning. The monoclinic phase exhibits approximate symmetry mimicking that of the supergroup Pna21 but with a metric symmetry that precludes true Pna21 symmetry. The structure of 2-amino-4′-chlorobenzophenone transitions to an incommensurately modulated phase upon cooling. The changes in the structure are attributed to slight conformational variations and a rearrangement of the hydrogen bonding networks in the structure in response to stimuli. The phase transition for 2-amino-4′-bromobenzophenone is classified as second order and a mechanism involving multiple coincident nucleation events is inferred from the conformational change and the incidence of twinning. The transformation of 2-amino-4′-chlorobenzophenone to an incommensurate phase is proposed to arise due to thermal contraction of the structure, which allows distinct competing hydrogen bonding networks between neighboring molecules to evolve.
Author(s): Attiwell L, Hill MT, Sellars JD, Palatinus L, Longcake A, Waddell PG
Publication type: Article
Publication status: Published
Journal: Crystal Growth and Design
Year: 2026
Volume: 26
Issue: 4
Pages: 1715-1728
Online publication date: 06/02/2026
Acceptance date: 02/02/2026
ISSN (print): 1528-7483
ISSN (electronic): 1528-7505
Publisher: American Chemical Society
URL: https://doi.org/10.1021/acs.cgd.5c01520
DOI: 10.1021/acs.cgd.5c01520
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