Ordered-disordered Structure Phase Transition And Dielectric Properties Of Small Molecule Amine Crystalline Compounds

Phase transition materials are sensitive to external stimulus,such as temperature,pressure,electric field,magnetic field,etc.,which permit a wide range of practical application in the electrical,optical,mechanical and magnetic field.Among them,inorganic materials have become one of the earliest and most widely used materials by virtue of their good electrical and thermal conductivity.However,owing to the disadvantages of high density,mechanical rigidity and difficulty in thin film fabrication,the utilization of inorganic ones on the next-generation functional materials have been severely hindered.Pure organic materials with the superiority of easy thin film fabrication,flexibility,low density and low cost,yet have been seriously limit due to their poor electrical and thermal conductivity for practical use.Within this context,organic-inorganic hybrid materials,combining the characterstics of both inorganic and organic components,have sparked growing interest in recent years.In order to design and explore new organic-inorganic hybrid phase transition materials,we usually select the nitrogen-containing small organic molecule groups as a building block,especially the ones with a spherical spatial configuration,which is easily for the construction of phase transition.Herein,10 novel crystalline compounds containing small amine cations were presented through the self-assembly method of nitrogen-containing organic small molecule groups and metal halides containing the elements of Cd,Cu and Mn:[(CH₃)₃NCH₂CH₃][Cd Cl₃](compound 1),[(CH₃)₃NCH₂CH₃]₂[Mn Cl₄](compound 2),[C₆H₁₄N][Cd Cl₃](compound 3),[C₆H₁₄N]₂[Cd Br₄](compound 4),[C₆H₁₀N₂][Cd Br₄](compound 5),[C₆H₁₀N₂][Cu Cl₄](compound 6),[C₆H₈N][Cd Br₃](compound 7),[C₆H₈N][Cd Cl₃](compound 8),[C₆H₈N]₂[Cu₃Cl₈](compound 9),[C₆H₈N]₂[Cu₃Br₈](compound 10).The synthesis process,IR spectrum,PXRD spectrum,crystal structure,and dielectric properties of these 10 crystalline compounds were presented to investigate their unique structures and peculiar physical properties.Strikingly,1 and 2 feature a significant dielectric anomalies,together with the DSC measurement,providing a solid proof for the existence of phase transitions.The reversible structural phase transitions occur at 363 K and 311 K for 1and 2,respectively.The mechanism of phase transition is mainly attributed to the ordered-disordered motion of[(CH₃)₃NCH₂CH₃]⁺cation,which is related to the contribution of the quasi-spherical cations.In addition,2 is in possession of a distinct photoluminescence phenomenon,where 2 appears light green and bright green under the condition of ambient light and ultraviolet light,respectively.Other crystalline compounds 3-10 have no obvious dielectric anomalies in the detectable temperature range,corresponding to the non-existence of phase transition.