Synthesis,characterization And Properties Of The Molecule-based Phase Transition Compounds Induced By Quinine Ring Derivatives

High-performance ferroelectric and dielectric phase transition materials are a type of functional materials with good application prospects in many fields such as aerospace,military and refrigeration equipment.From the current point of view,the research and development of molecular-based phase transition materials with high-performance ferroelectric and dielectric properties are still in the development stage.On the basis of previous literatures,we chemically modified the nitrogen atom of the highly symmetric heterocyclic ligand 1-azabicyclo[2.2.2]octane,and synthesized three quinine ring ligand-based amine salt in order to find new types of ferroelectric and dielectric materials.Eight organic-inorganic hybrid molecular-based phase transition compounds were prepared using three quaternary amine salts as templates.The phase transition temperature,molecular structure before and after the phase transition,and ferroelectric,dielectric,and fluorescent properties were studied.1.Using[?CH₃?₂CH-C₇H₁₃N]⁺·Br^–as the building unit,the crystals were cultured with Co Br₂,Mn Br₂,Mn Cl₂and Zn Br₂by solution volatilization to obtain four molecular-based phase transition compounds:[?CH₃?₂CH-C₇H₁₃N]₂Co Br₄?1?;[?CH₃?₂CH-C₇H₁₃N]₂Mn Br₄?2?;[?CH₃?₂CH-C₇H₁₃N]₂Mn Cl₄?3?and[?CH₃?₂CH-C₇H₁₃N]₂Zn Br₄?4?.DSC and variable temperature single crystal structure analysis tests have determined that all four compounds underwent structural phase transitions.The phase transition temperatures are 228 K,226 K,236 K and 230 K,respectively.Variable temperature single crystal X-ray diffraction shows that these four compounds are homologues.These four compounds underwent phase transitions from LTP with a non-centrosymmetric space group of Cc?No.9?in monoclinic system to RTP with a centrosymmetric space group of C2/c?No.15?in monoclinic system.The twist of the quinine ring causes a phase transition.According to the dielectric test results,it was found that they had a dielectric dissimilarity near the phase transition point.Compound 1 has ferroelectric properties with a saturation polarization value of 0.67?C/cm²and a residual polarization of about 0.19?C/cm².In addition,variable temperature SHG effects of compounds 1,2 and 3 were also studied.The test results show that all three compounds have SHG responses.Fluorescence test results show that compounds 2 and 3 have green fluorescent properties at room temperature.2.Using[CH₃-C₇H₁₃N]⁺·Br^–as the building unit,and react with Co Br₂and Mn Br₂,respectively,to obtain two phase transition compounds 5 and 6 by solution self-assembly:[CH₃-C₇H₁₃N]₂Co Br₄?5?and[CH₃-C₇H₁₃N]₂Mn Br₄?6?.DSC test results show that compounds 5 and 6 underwent structural phase transformations near 273 K and 277 K,respectively.Analysis of the crystal structure by a variable temperature X-ray single crystal diffractometer test confirmed that compounds 5 and 6 were homologues.These two compounds underwent phase transitions from LTP with a chiral space group of P2₁2₁2₁?No.19?in orthogonal system to RTP with a space group of Pnma?No.62?in orthogonal system.During the cooling process,the values of a and b in the unit cell parameters of the two compounds are interchanged.Compounds 5 and 6 also have good dielectric properties and low dielectric loss.3.Using[CH₃?CH₂?₃-C₇H₁₃N]⁺·Br^–as the building unit,react with Co Cl₂and Zn Cl₂respectively to obtain two ionic phase transition compounds 7 and 8 by solution method:[CH₃?CH₂?₃-C₇H₁₃N]₂Co Cl₄?7?and[CH₃?CH₂?₃-C₇H₁₃N]₂Zn Cl₄?8?.The DSC test confirmed that the two compounds had a reversible phase transition in the heating-cooling mode.The phase transition temperatures of compounds 7 and 8 were 329 K and 328 K,respectively.Variable temperature single crystal structure analysis tests showed that the compound 7 underwent phase transition from HTP with a space group of P4₁2₁2 in orthogonal system to RTP with a space group of P4₃in orthogonal system.The compound 8 underwent phase transition from HTP with a space group of P4₃2₁2 in orthogonal system to RTP with a space group of P4₁in orthogonal system.Through the study of the dielectric properties of the two compounds,it was found that compounds 7 and 8 both experienced a dielectric mutation near the phase transition point,and these two compounds had large dielectric constant.This indicates that compounds 7 and 8 can be tunable dielectric materials as well as reversible phase transition materials.