Browsing by Author "Haynes, Delia A."

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    Lack of co-crystal formation with cyclotriphosphazenes : a cautionary tale
    (South African Chemical Institute, 2016) Wahl, Helene; Haynes, Delia A.; Le Roex, Tanya
    ENGLISH ABSTRACT: The attempted formation of co-crystals with a series of cyclotriphosphazene derivatives has been investigated. Despite numerous attempts, only one co-crystal was obtained. The crystal structure of this material, [hexakis(4-pyridyloxy)-cyclotriphosphazene][ terephthalic acid]2.5, is presented here. The crystal structures of 2,2-bis(4-formylphenoxy)-4,4,6,6-bis[spiro(2’,2”-dioxy- 1’,1”-biphenylyl]cyclo-triphosphazene and hexakis(4-cyanophenoxy)cyclotriphosphazene are also reported for the first time. The extremely low rate of co-crystal occurrence in these materials cannot be explained, despite the consideration of several possibilities. This serves as a cautionary tale – co-crystal formation is not necessarily straightforward.
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    Mechanically compliant single crystals of a stable organic radical†
    (Royal Society of Chemistry, 2021-03) Commins, Patrick; Dippenaar, A. Bernard; Li, Liang; Hara, Hideyuki; Haynes, Delia A.; Naumov, Pance
    Mechanically compliant organic crystals are the foundation of the development of future flexible, light-weight single-crystal electronics, and this requires reversibly deformable crystalline organic materials with permanent magnetism. Here, we report and characterize the first instance of a plastically bendable single crystal of a permanent organic radical, 4-(4′-cyano-2′,3′,4′,5′-tetrafluorophenyl)-1,2,3,5-dithiadiazolyl. The weak interactions between the radicals render single crystals of the β phase of this material exceedingly soft, and the S–N interactions facilitate plastic bending. EPR imaging of a bent single crystal reveals the effect of deformation on the three-dimensional spin density of the crystal. The unusual mechanical compliance of this material opens prospects for exploration into flexible crystals of other stable organic radicals towards the development of flexible light-weight organic magnetoresistance devices based on weak, non-hydrogen-bonded interactions in molecular crystals.