| The internal crystal structure and macroscopic properties of phase-transition materials are changed driven by physical or chemical factors（temperature,pressure,electric field）without changing the chemical composition.In recent years,phase-transition materials have drawn increasing concern owing to the appreciable applications in sensors,nonlinear optical devices,switchable dielectric devices,actuators and data storage.Wherein,the dielectric constants of the dielectric-switching phase-transition materials can switch between high and low dielectric states with temperature changing.Currently,many scholars have conducted in-depth research on the structural design and multifunctionality of dielectric-switching phase-transition materials.The construction of compounds containing moving or flexible parts,which enable distortion or conformational changes,is a viable method for obtaining phase-transition materials.Organic-inorganic hybrid materials are much-anticipated phase transition materials,because they contain inorganic skeletons with excellent properties（thermal stability,band gap tunability,excellent electrical transfer,easy deformation,etc.）and cations which are removable and modifiable.Among them,the design of organic parts has attracted the attention of many scholars in order to obtain multifunctional phase transition materials.For example,the introduction of quasi-spherical organic ligands can easily lead to phase transitions and introducing halogen atom（F,Cl or Br）into quasi-spherical organic ligands generated new ferroelectric and ferroelastic material with greatly increased phase transition temperatures.It is known that thioether groups have the ability to absorb soft metal ions as a strong soft organic ligand.Many researchers have introduced thioether groups into metal organic frameworks（MOFs）systems for the purpose of metal Pd adsorption.Inspired by this,this paper introduced thioether groups into organic amine molecules,which are susceptible to structural phase transition stimulated by temperature.The thioether groups exert their properties as donors for the adsorption of precious metals,but phase transition behavior will disappear after adsorption.Based on this,it is possible to monitor the adsorption of metals through the changes of the dielectric properties of materials.In this paper,the protonated N-（2-hydroxyethyl）thiomorpholine,2-methyl-2-thiazoline and thiomorpholine were used as cations to synthesize the following eight compounds with inorganic metal salts:[（C2H4OH）C4H9NS]Cd Cl3（1）、[（C2H4OH）-C4H9NS]Zn Br3（2）、[（C2H4OH）C4H9NS][Cd（SCN）3]（3）、[C4H8NS]2Mn Br4（4）、[C4H8NS]3Bi2Br9（5）、[C4H8NS]Sb Cl4（6）、[C4H10NS]2[Cl O4]2·H2O（7）and[C4H10NS]2Zn Cl4（8）.The structure,phase transition behavior,dielectric properties and adsorption properties of crystalline compounds were studied by a series of characterization methods.The main research content of this paper is divided into the following three parts.（1）the chapter 3,the preparation and dielectric properties of hybrid compounds containing N-（2-ethyl-hydroxyl）thiomorpholine are studied.Compounds 1,2,and 3 were synthesized by mixing N-（2-hydroxyethyl）thiomorpholine hydrobromate with metal salts.Both of compounds 1 and 3 are consisted of one-dimensional chains,however,the compound 2 is zero-dimensional structure.Compound crystallizes in chiral space group with corresponding SHG response signal.And 1 exhibits reversible phase-transition behavior at 174.4/162.8 K,while compounds 2 and 3 have no phase-transition behavior.The microscopic cause of phase transition can be determined as the joint movement of metal skeleton and organic cation.For compound 2,the central Zn of the metal skeleton is coordinated with the S atom of the organic cation so that it cannot produce strong interaction force with Pd（II）and cannot show adsorption properties.Therefore,the adsorption capacity for metal Pd is:3>1>2.And the adsorption performance of compound 1 was monitored by the presence of dielectric switch and SHG signal.（2）Chapter 4,the preparation and dielectric properties of hybrid compounds2-methyl-2-thiazoline complexes are studied.Compounds 4,5 and 6 are zero-dimensional complexes composed of protonated 2-methyl-2-thiazoline cations.Compounds 4 and 5 exhibit reversible phase transition behavior at 377.2/360.1 K and380.1/361.9 K,respectively.However,it is difficult to investigate the microscopic mechanism of phase transition because the phase transition temperature is close to the melting point.Driven by temperature,compound 6 has no phase-transition behavior and no corresponding dielectric properties.However,they can adsorb heavy metal Pd with adsorption capacity:6>4>5.The phase transition behavior and dielectric properties of compounds 4 and 5 can be used to monitor metal adsorption.（3）Chapter 5,the preparation and dielectric properties of hybrid compounds thiomorpholine complexes are studied.Compounds 7 and 8 are zero-dimensional organic-inorganic hybrid compounds containing thiomorpholine.Compound 7 has reversible phase-transition behavior at 218.2/202.2 K.And the reason for phase transition is the movement of anionic skeleton.Compound 8 has no phase-transition behavior.In this paper,the introduction of functional groups（thioether groups）in cycloamine cations has great significance for the construction of new multifunctional phase-transition materials. |
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