Synthesis, Characterization And Phase Transition Properties Research On A Series Of Derivatives Based On DABCO

Phase transition materials have wide application prospects in many fields such as energy, aerospace and building, in recent years, research on phase transition materials is gradually increasing. In order to find more novel phase transition materials, on the basis of reading a lot of literature about phase transition materials, three kinds of quaternary ammonium salt based on Dabco were synthesized with chemical modification of the high symmetry ligand 1,4-diazabicyclo[2.2.2]octane(Dabco), and we synthesized a series of phase transition compounds based on the quaternary ammonium salt, the phase transition point,molecular structures of in two phases and dielectric properties of the compounds were further studied.1. Three metal-organic coordination compounds with phase transition properties were prepared by the self-assembly of(Dabco-CH2Cl)+·Cl- and transition metal ions M2+(M = Cd, Cu, Mn) respectively. [Cl2Cd(Dabco-CH2Cl)]2·(μ-Cl)2(1); Cu(Dabco-CH2Cl)(H2O) Br2.75Cl0.25(2); Mn(Dabco-CH2Cl)Cl3H2O(3). The phase transition temperature and crystal structures of the three compounds in two phases were confirmed by DSC measurements and variable temperature single crystal structure analysis, further more, dielectric properties have been further studied separately. Among which, the DSC result of 1 shows that the compound occurs phase transition when the temperature cooling to 157.1 K, single crystal structure in both room temperature phase(293 K) and low temperature phase(100 K) were determined by single crystal structure test, at the same time, dielectric response of the compound is evident around phase transition point, there were ladder-like dielectric anomaly in the process of both cooling and heating. DSC results show that compounds 2 and 3 underwent a phase transition at 181 K and 186.7 K respectively. Variable temperature single crystal structure analysis showed that the two compounds are all crystallized in orthorhombic system space group Pnma in room temperature phase, and translated to monoclinic system space group P21/n in low temperature phase. The ordering of twisting motions of 1,4-diazoniabicylo[2,2,2]octane ring was the main reason that cause the phase transition.2. Two organic molecular-ionic compounds with structural phase transition were obtained from the ligand(Dabco-CH2Cl)+·Cl- with perchloric acid and tetrafluoroboric acid respectively. C7H15ClN22+·2ClO4-(4);(C7H15ClN22+)3·(BF4-)4·2Cl-(5). DSC results showed that the compound 4 underwent a phase transition when the temperature cooling to 143.9 K, and showed a stronger dielectric response near the phase transition point. Variable-temperature single crystal structural analysis showed that the compound crystallized in the orthorhombic system Pbca space group at 291 K and 170 K, and monoclinic system P21/c space group at 100 K. Dabco ring in high temperature phase were highly symmetry, and the perchlorate were serious disordered. When the temperature dropped to phase transition point, Dabco rings occurred distorted and most disordered perchlorate changed to orderly. Compound 5 underwent a reversible phase transition when the temperature cooling to 242.9 K, the compound crystallized in orthorhombic system space group Pnma in room temperature phase, and translated to monoclinic system space group P21/c in low temperature phase, and the result has been further confirmed by dielectric measurement. The order-disorder transition of BF4- anions and the ordering of twisting motions of Dabco ring were the main cause of the phase transition.3. One organic molecular-ionic compound with structural phase transition was obtained from the(CH3-Dabco-CH3)2+·2Br- ligand with perchloric acid: C8H18N22+·2ClO4-(6). Compound 6 undergo a phase transition at 201.7 K. the compound crystallized in orthorhombic system space group Pnma in room temperature phase, and translated to monoclinic system space group P21/c in low temperature phase. And the result has been further confirmed by dielectric measurement, and the order-disorder transition of ClO4- anions and the ordering of twisting motions of Dabco ring caused the phase transition.4. Three metal-organic coordination compounds with phase transition properties were prepared by the self-assembly of the ligand [(CH3)2CH-Dabco-CH(CH3)2]2+·2Br- and transition metal ions M2+(M= Mn, Co, Zn) halogen atoms replaced by Br and Cl atoms and the ordering of twisting motions of Dabco ring caused the phase transition of compounds 7, 8, 9.