Synthesis And Characterization Of Spin Crossover Complexes Based On Amine Ligand

Under external stimulation,the physical and chemical properties of the spin crossover complex will also undergo corresponding changes,such as structural changes,magnetic and thermodynamic changes,and changes in response to the object.Because of its controllable structure,easy processing and bistable state,the spin crossover complex has a very broad application prospect.At present,most of the most widely studied complexes are Fe N₆ type spin crossover complexes constructed with Fe（Ⅱ）as the central metal ion.In this paper,the spin crossover properties of Fe（Ⅱ）complexes are studied based on amine ligands.This paper is mainly divided into four chapters:The first chapter is the preface,which systematically introduces the characteristics,research progress,characterization methods and cultivation methods of single crystal.At last,the thesis expounds the idea of topic selection and research content.In the second chapter,the spin crossover complex[Fe（L-NH₂）₂]·H₂O（1）and its response to acid,base,formaldehyde and common volatile solvents were studied.Single crystal X-ray diffraction results showed that the complex 1 was the expected mononuclear molecular structure.The magnetic susceptibility measurement and differential scanning calorimetry showed that the complex 1 exhibit one-step slow spin crossover behavior and its transition temperature was 320 K.Complex 1 can produce reversible response behavior to acid and base stimulation in solid phase and liquid phase.Under the action of acid,the complex will partially dissociate and cause the metal center to change from a low spin state to a high spin state,while the base can restore the original coordination structure and magnetic behavior.And the acid base action is accompanied by the obvious color change of the complex.In addition,the complex is able to show distinct responses toward formaldehyde and protic and nonprotic vapors,as a result of the different affinity of the amino functional group with those chemicals.In the third chapter,six new complexes were synthesized:[Fe^2MeL_quinoline（NCS）₂]（2）,[Fe^2MeL_quinoline（NCSe）₂]（3）,[Fe^2MeL_quinoline（NCBH₃）₂]（4）,[Fe^DibenzylL（NCS）₂]（5a）,[Fe^DibenzylL（NCS）₂]（5b）,[Fe^DibenzylL（NCSe）₂]（6）,[Fe^DibenzylL（NCBH₃）₂]（7）,wherein 5a and 5b are a group of polymorphs.Single crystal X-ray diffraction and magnetic susceptibility measurements confirmed that complexes 2,3,4,5b and 6 were stable in high spin state,and that both 5a and 7 had a gradual spin crossover behavior with transition temperatures of 81 K and 183 K,respectively.Through the research of 16 which have been reported in the known literature related complexes[Fe L（NCE）₂]（E=S,Se,BH₃）and 2-7with similar structures,the relationship between the spin crossover behavior and the structure of this type of complex was proposed:compared with the tetradentate ligand and crystal accumulation,co-ligand NCE^-played a more important role in the regulation of the spin crossover transition temperature.[Fe^2MeL_quinoline（NCE）₂]is the only exception due to its significant steric effect,hence inhibits the occurrence of spin crossover properties even in the presence of a strong co-ligand NCBH₃^-.The fourth chapter is the summary and prospect of the above work.