Design And Synthesis Of Homochiral Quasi-Spherical Molecular Hybrid Phase Transition Materials

Due to the many physical properties of phase transition materials,such as thermal,optical,electrical,magnetic,and polarization,which can change with temperature,they have been significantly applied in sensors,nonlinear optical devices,switchable dielectric devices,drivers,and data storage,and have attracted more and more attention in recent years.Compared to the basic properties of inorganic or dopants,the progress of organic-inorganic hybrid phase transition materials relies on exploring new families.Unfortunately,due to the lack of effective measures to control and optimize the performance of phase transition materials,searching for multifunctional phase transition materials with excellent properties is like looking for a needle in a haystack.According to the research,the introduction of chirality into organic molecules can effectively make organic-inorganic hybrid perovskite materials crystallize in the chiral space group,and the"quasi spherical theory"can promote the phase change behavior.Guided by the introduction of chirality and the"quasi spherical theory",an alkali metal phase transition materials was synthesized by designing and synthesizing homochiral quasi spherical molecules（1S,4S）-2,5-diazabicyclo[2.2.1]heptane,and reacting them with alkali metal halide salts Cs Cl,Cs I,KBr,KI,Na Br to obtain[2,5-2.2.1-Hdabch]Cs Cl₃·0.25H₂O（1）,[2,5-2.2.1-Hdabch]Cs I₃（2）,[2,5-2.2.1-Hdabch]KBr₃·0.5H₂O（3）,[2,5-2.2.1-Hdabch]KI₃（4）,[2,5-2.2.1-Hdabch]Na Br₃（5）,and with non-metallic NH₄X（X=Cl,Br,I）,HI to obtain non-metallic phase transition materials[2,5-2.2.1-Hdabch]NH₄Cl₃·0.5H₂O（6）,[2,5-2.2.1-Hdabch]NH₄Br₃·0.5H₂O（7）,[2,5-2.2.1-Hdabch]NH₄I₃（8）,[2,5-2.2.1-Hdabch]I₂（9）,and reacted it with semiconductor metal salts Sn X₄（X=Cl,Br）to obtain phase transition materials[2,5-2.2.1-Hdabch]Sn Cl₆·3H₂O（10）and[2,5-2.2.1-Hdabch]Sn Br₆（11）.A series of characterizations such as differential scanning calorimetry（DSC）,second harmonic generation（SHG）and temperature dependent dielectric were carried out on these compounds.It was found that 11compounds all had reversible structural phase transitions,of which 6～8 had phase transition temperatures of 349.0 K,362.3 K and 397.0 K,10 and 11 had phase transition temperature of 267.5 K and 286.0 K,respectively.The phase transition temperature increased with Cl,Br and I,This confirms the rule that replacing halogen anions can effectively increase the phase transition temperature of compounds.And compounds 1,3,and 5 exhibit reversible dielectric anomalies,while compounds 1,2,9,and 11 exhibit reversible SHG effects,all of which are multifunctional phase transition materials.Compounds 1,3,4,6,7 and 9 were crystallized in P2₁2₁2₁at room temperature,compound 2 was crystallized in P6₃22 space group at room temperature,compound 5 was crystallized in P6₅22 space group at room temperature,compound 8 was crystallized in P3₂21 space group at room temperature,and compound 10 was crystallized in P2₁space group at room temperature,all of which are chiral space group.And P2₁is a ferroelectric space group.Because the phase transition point of compound 10 is below room temperature,it is very likely that the compound is an antiferroelectric.It is worth noting that compounds 3,6,7,and 8have a three-dimensional structure,indicating that the size of[2,5-2.2.1-Hdabch]²⁺organic amine cations is appropriate and can be used to construct three-dimensional perovskite materials.This article introduces chirality into organic amine molecules and designs and synthesizes chiral quasi spherical small molecules（1S,4S）-2,5-diazabicyclo[2.2.1]heptane based on the"quasi spherical theory".It reacts with alkali metal salts,ammonium halides,hydrogen halides,and tin salts,and successfully obtains 11 phase transition materials,of which six are multifunctional phase transition materials.The fact has proven that introducing chirality and the"quasi-spherical theory"is a practical and effective means.Replacing halogen anions can increase the phase transition temperature,which to some extent enriches the design and synthesis of multifunctional phase transition materials.