Synthesis And Characterization Of Spin Crossover Complexes Based On Pyridine-Fatty Amine Tetradentate Ligand

Spin crossover complexes with bistable properties have potential applications in many areas,such as memory cells,sensors,actuators and displays.The spin crossover complexes constructed by Fe（II）as the central metal ion are the research hotspots of today’s bistable molecular magnetic materials.This paper focuses on the construction and characterization of Fe（II）spin crossover complexes based on pyridine-fatty amine tetradentate ligands.The full text is divided into four chapters:The first chapter is the introduction.Firstly,the spin crossover complexes occupying an important position in molecular-based magnetic materials are introduced.Then,the properties,development process of spin crossover complexes,several important characterization methods and preparations are described.Finally,the topic and the content of the research are explained.The second chapter describes the preparation,characterization and properties of a series of complexes[Fe(L_Cl)（NCE）₂]（E=S,Se,BH₃）.The three complexes are synthesized by iron（II）salt,main ligand L_Cl（N,N’-Bis[（4-chloro-2-pyridyl）methyl]ethylene-1,2-diamine）and three different ancillary ligands KSCN,KSeCN and NaNCBH₃.The single crystal diffraction analysis indicated that the three derivatives were heterogeneous isomorphous structures,and the replacement of the ancillary ligand did not change the packing arrangement between the[FeL（NCE）₂]molecules.The results of magnetic susceptibility study indicate that the complex[Fe(L_Cl)（NCS）₂]maintains high spin in the 10-300 K temperature range and replaces the ancillary ligand with NCSe^-,which can make the complex have a spin crossover properties and the spin-transition temperature is around 177 K,and the replacement with NCBH₃^-can further increase the spin-transition temperature by about 30 K.Therefore,in the case of constant molecular packing structure,we achieved the regulation of the self-rotation temperature of the complex by replacing NCS^-,NCSe^-and NCBH₃^-ligands.The third chapter describes the preparation,characterization and properties of a five-nuclear complex[Co^II(^2MeL_pz)]₃[Co^III（CN）₆]₂ and three Fe（II）-doped isomorphous complexes[Fe_x^IICo^II_3-x(^2MeL_pz)₃][Co^III（CN）₆]₂（x=2.1,1.5 and 0.9）.The above four complexes are all synthesized by cobalt（II）salt or iron（II）salt,the main ligand^2MeL_pz（N,N’-dimethyl-N,N’-bis（2-pyrazinylmethyl）-1,2-ethanediamine）and the ancillary ligand NaNCBH₃ through hydrothermal method.These five-nuclear complexes are isomorphic by single crystal diffraction analysis,and they all have a molecular geometry of a triangular double cone.For pure Co complexes,Co（III）ions occupy the axial position of the triangular bifurcation,and Co（II）ions occupy the equator position.The results of magnetic susceptibility study show that the axial Co（III）adopts a low spin electron configuration,while the Co（II）ion on the equatorial plane is in a high spin state throughout the temperature range.By doping Fe（II）,Fe（II）replaces some of the Co（II）ions and exhibits a spin crossover property with a transition temperature of 168 K.By controlling the ratio of Fe（II）doping,it is possible to control the proportion at which the spin-transformation occurs,while the transition temperature is not affected.The fourth chapter gives a detailed summary of the work done above and looks forward to it.