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Design and understanding of solid-state and crystalline materials



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CrystEngComm, 2009, 11, 1240 - 1244, DOI: 10.1039/b822832a

Halogenoxygen aggregation and disorder modes in pressure frozen XCF2CF2X:1,4-dioxane (X = Br,I) complexes

Anna Olejniczak, Andrzej Katrusiak and Ashwani Vij

Formation of cocrystals and halogenO interactions was studied in the structures of 1,4-dioxane with 1,2-diiodo-, 1-bromo-2-iodo- and 1,2-dibromoperfluoroethanes. Mixtures pressure-frozen in a diamond-anvil cell have been investigated. Structures of cocrystals of 1,2-diiodoperfluoroethane:1,4-dioxane at 0.30(5) GPa/296(2) K and of 1-bromo-2-iodoperfluoroethane:1,4-dioxane at 0.62(5) GPa/296 K were determined by single-crystal X-ray diffraction. Also the single-crystal of 1,4-dioxane separated from its mixture with 1,2-dibromoperfluoroethane, which remained liquid, was investigated at 0.42 GPa/296 K. The cocrystal of ICF2CF2I:C4H8O2 and the C4H8O2 crystals freeze into the same phases as those obtained by cooling; the BrCF2CF2I:C4H8O2 cocrystal was not synthesized before. In all these cocrystals the structures are dominated by halogenO interactions. In the structure of ICF2CF2I:C4H8O2 the –CF2–CF2– moiety is disordered about the II molecular axis and the C4H8O2 molecule rotates about the OO axis, too; in BrCF2CF2I:C4H8O2 the Br and I atoms are disordered at the same position with half occupancy, but the C4H8O2 molecule is ordered. The pressure-freezing of 1,4-dioxane from the BrCF2CF2Br:C4H8O2 mixture yielded ordered phase II of 1,4-dioxane previously obtained from the neat compound by cooling. Spectacular kinetic crystallization of ICF2CF2I:C4H8O2 in the form of hexagonal snowflakes has been observed in the diamond-anvil cell.

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