Journal
CRYSTAL GROWTH & DESIGN
Volume 13, Issue 9, Pages 4110-4117Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cg4009202
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Funding
- Umm Al-Qura University, Saudi Arabia
- Cardiff University
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We report the discovery of a rare case of polymorphism among trans-cinnamic acid derivatives in which both polymorphs are classified as beta-type structures based on their solid-state structural properties and their solid-state photoreactivity. Specifically, for 3-fluoro-trans-cinnamic acid, crystallization from many solvent systems leads to formation of one polymorph (denoted beta(1)), although, in a few cases, concomitant crystallization of another polymorph (denoted beta(2)) is also observed. On heating the beta(1) polymorph, a solid-state phase transition occurs at ca. 119 degrees C to produce the beta(2) polymorph. This polymorphic phase transition is irreversible, and the beta(2) polymorph remains stable on subsequent cooling to ambient temperature. Both the beta(1) and the beta(2) polymorphs undergo a topochemical [2 + 2] photodimerization reaction upon UV irradiation to produce 3,3'-difluoro-beta-truxinic acid as the photoproduct in almost 100% yield. However, these reactions are associated with complete loss of crystallinity, preventing the structural properties of the directly produced solid photoproduct from being determined by single-crystal or powder X-ray diffraction techniques.
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