Synthesis And Characterization Of Thermochromic Spin Crossover Complexes

The research of spin crossover complexes is of great significance to the development of new-generation molecular sensors and information storage devices,and has become a hotspot in the field of magnetic research.Although there have been many advances in the study of spin-crossover fields in recent years,there are still many problems that need to overcome,such as finding more spin-crossover systems that can meet the requirements of industrial applications,realizing multi-functionalization of spin-crossing complexes,the manipulation of spin-dependent conditions,the effect of supramolecular interactions on spin-crossover,and so on.Therefore,this article focuses on the synthesis of spin-spin coordination complexes of divalent iron,and it is expected that the spin-transition system with application value can be obtained by improving the synergistic effect of the system.Four chapters are included in the dissertation.In chapter 1,the background and the research progress of spin crossover switchable molecular materials were accounted.In chapter 2,N,N’-dimethyl-N,N’-bis（2-pyridylmethyl）-1,2-ethanediamine was used as the tetradentate ligand,in addition,we further control the spin-crossover properties by changing the secondary ligands,for example,using monodentate ligands of NCX-(X = S（1）,Se（2）,BH₃（3）and BPh3（4）.At last,a spin-crossover magnetic material with hysteresis can be formed.The results show that 2a in these complexes exhibits two-step spin transition and has a LIESST effect at low temperature.The polymorph 2b of 2a is also synthesized unexpectedly,which keeps the high spin state at the test temperature.The complexes 1 and 3 always maintain a high spin state,while the complex 4 always remains in a low spin state at the test temperature range.In addition,their structures and properties are studied in detail,and the effects of structural differences on magnetic properties are discussed.In chapter 3,based on the development of the previous chapter,a series of complexes[Fe（bqdmen）2（NCX）₂]（bqdmen = N,N’-dimethyl-N,N’-bis（2-quinolylmethyl）-1,2-ethanediamine,X = S（5）,Se（6）and BH₃（7））were synthesized.It was found that all of the three complexes exhibit high spin states in the range of the test temperature.Their structures and properties are studied in detail,and the reasons for the disappearance of spin-crossover behavior are also discussed.In chapter 4,the whole thesis work is summarized and forecasted.