The Structure And Phase Trantion Properties Of Organic-inorganic Hybrid Compounds Based On Halogen Substitution Of Tetramethylphosphine

Organic-inorganic hybrid compounds combine the excellent properties of both organic and inorganic components.They have attracted widespread attention due to their molecular flexibility and diversity.Besides,the method of replacing the cation with a halogen group have important significance for the functional regulation of hybrid molecules.In order to explore more coordinated multifunctional phase change materials,we have coordinated trimethylphosphine derivatives with inorganic metal anions and successfully synthesized 8new organic-inorganic hybrid compounds:[（CH₃）₃PCH₂F]₂[CdBr₄]（1）,[CH₃PCH₂Cl][Fe Cl₄]（2）,[（CH₃）₃PCH₂F][Cd Cl₃]（3）,[（CH₃）₄P][Cd（SCN）₃]（4）,[（CH₃）₃PCH₂F][Cd（SCN）₃]（5）,[（CH₃）₄P][PbBr₃]（6）,[（CH₃）₃PCH₂F][PbBr₃]（7）and[（CH₃）₃PCH₂Cl][PbBr₃]（8）.Herein,focusing on the crystal structure,phase transition behavior and other physical properties,a series of studies and discussions were conducted on organic-inorganic hybrid compounds.It is mainly divided into three parts:（I）In Chapter III,low-dimensional organic-inorganic hybrid crystals are designed and synthesized based on halogen-substituted trimethylphosphine derivatives.According to the results of X-ray single crystal diffraction and dielectric test,it can be preliminarily judged that compounds 1-3 undergone one or two structural phase transition.Fortunately,the crystal structures of compound 3 are obtained in all three phases.It can be concluded from the structural comparison that the phase transition occurs mainly due to the order-disorder movement of the cations.（Ⅱ）In Chapter IV,research on the regulation of ferroelasticity of organic-inorganic hybrid perovskites.An organic-inorganic perovskite compound 4 and its fluorine-substituted product compound 5exhibit ferroelastic phase transitions above room temperature.The very close van der Waal radii of H and F atoms ensures the ferroelasticity.The higher electronegativity of F atom increases the phase transition temperature from 308 K in compound 4 to 318 K in compound5 and the value of spontaneous strain improved by 38.6%.The dielectric change multiple of 5is 23.38%larger than that of 4 accompanied with phase transition.（Ⅲ）In Chapter V,the study of band gap regulation of organic-inorganic hybrid perovskite semiconductor materials.Considering the results of single crystal structure analysis,DSC and dielectric test,there is a phase transition in compounds 6-8,respectively.The introduction of heavier halogen atom（F or Cl）to[Me₄P]⁺increases the potential energy barrier required for the tumbling motion of the cation,hence achieving the transformation of the phase transition temperature from low temperature（192 K）to room temperature（285 K）and high temperature（402.3 K）.Besides,the optical band gaps reveal a broadening trend with 3.176 e V,3.215 e V and 3.376 e V along the H→F→Cl series,which is attributed to the formation of the structural distortion.