The Synthesis, Structure And Property Investigations Of New Molecular Phase Transition Compounds Constructed By The Disordered Group

Various designing approaches have been developed to induce thesolid-to-solid phase transitions. From the point of the molecular design, introductionof disordered groups into the molecular crystals is one of the most effective strategies,since the order-disorder transformation plays an important role in structural phasetransitions. That is, the disordered groups may easily cause the solid-to-solid phasetransition. We have successfully built the five phase transition compounds byintroduction the disordered groups trifluoromethanesulfonic acid、diisobutylamine、chlorodifluoroacetic acid:(C10H16N)+·CF3SO3(1)、diisobutylammonium L-tartaricacid(2)、diisobutylammonium maleic acid(3)、betaine chlorodifluoroacetate(4). Wehave systematically researched the crystal structure、thermodynamic and dielectricproperties of these compounds.1. The compound (C10H16N)+·CF3SO3has been synthetized with theN-isopropylbenzylamine and trifluoromethanesulfonic acid in the solution of theethanol and water. We confirmed the phase transition temperature at189.7K by theDSC measurement. The crystal structures were collected at273K、100K, respectively.We have analyzed the two different temperature crystal structures. According to thecrystal structure analysis,1crystallize both in the orthorhombic, space group Pbca.The crystal structure analysis reveals that the anionic moiety of1becomes much moreordered when the temperature decreasing. We found that the phase transition anddielectric anomalies are induced by the slight orderings and the relative twistingmotions of the isopropyl groups in cationic parts. These research results will provide anew method for constructing the phase transition materials. 2. We have successfully built the novel phase transition compounddiisobutylammonium L-tartaric acid(2) utilizing the disordered group diisobutylamineand the L-tartaric acid. We have determined the phase transition temperature at-141℃by the DSC measurement. The X-ray single-crystal diffraction confirmed theroom temperature and low temperature crystal structures of the compound2. Thestructure at room temperature crystallizes in P21212, while space group belongs to thespace group P212121in the low temperature. By the crystal structure comparison, wedrew the conclusion that the order-disorder motion of the hydrogen bond is mainlyresponsible to the phase transition.3. By the crystal engineering and molecular designing, we construct thephase transition material diisobutylammonium maleic acid with the disordered groupdiisobutylamine cation and maleic acid(3).Variable temperature dielectricmeasurement verified that the compound has experienced the phase transition. It isvery regretful that we only obtained the room temperature crystal structure. Thus, wecan’t explain the phase transition mechanism from the change of the structure.4. We have assembled the new phase transition compound(C5H12NO2)+·ClF2COO-(4) by introducing the disordered group chlorodifluoroaceticacid and the classical glycine betaine cation. By the DSC measurement, we haveascertained the phase transition temperature at132.7K and determined the crystalstructures at293K and100K. The room temperature space group belongs toP21/m,while the low temperature space group is Cc. This is a typical ferroelectricphase transition from the centrosymmetric point group to the noncentrosymmetricalpoint group, belonging to the one of the88kinds ferroelectric phase transitions,according with the Landau theory. The order to disorder motion of the fluorine atomin the anion is the main reason for triggering the ferroelectric phase transition.