Novel local D-A interactions and physical properties in organic mixed crystals

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Local D-A interactions and some physical-chemical properties in mixed crystals of organic compounds were investigated. The materials studies were derivatives of triptycene, azulene, 4-substitutedbenzyl alcohols and alkyl urea.A new method of preparation of triptycenequinone (TPQ)/triptycenehydroquinone (TPHQ) mixed crystal was found. Crystal structures were determined for bis-(Bromomethyl)triptycene (bis-BrMe-TPQ) and its several clathrates. A mixed crystal of the compound with bis-(bromomethyl)triptycenehydroquinone (bis-BrMe-TPHQ) exhibited local D-A interaction.Four membered ring type H-bond systems and phase transition were found for bis-(hydroxy)triptycenes. From the knowledge of the crystal structure, an interesting dielectric property is expected for its mixed crystal with hydroxytriptycene.The crystal structure of 6,7-dimethoxytriptycene suggests that it cannot form a TPQ/TPHQ type mixed crystal. X-ray structure of 5,12-dihydro-o-5,12-benzenonaphthacne-1,4-dione revealed the presence of its clathrate with benzene and this result indicates that a local D-A interaction in a mixed crystal would be possible by changing the guest from benzene to other methyl-benzenes.For mixed crystals of p-substitutedbenzyl alcohols, composition dependence of the characteristics of the phase transitions, as well as an isotope effect on the transition behavior, were investigated in detail. These results contributed to elucidate the transition mechanism of the compounds.Among a series of alkyl-ures, octyl-urea exhibited a novel phase transition accompanied by a very large enthalpy change. Mixed crystals of octyl- and heptyl-urea were found to show a transition characteristic that was very dependent on the composition, giving useful information on the transition mechanism.