Design And Synthesis Of Tetradentate Nitrogen-containing Heterocyclic Compounds And Construction Of Their Spin Crossover Complexes

Nitrogen-containing heterocyclic compounds are widely used in the fields of pesticides,medicine and multi-functional materials.Because the nitrogen atom in its structure contains lone pair electrons.It can be used as a Lewis base to coordinate with metal ions,and the obtained complexes have a broad application prospect in the fields of molecular switches,information storage,sensors and other high-performance devices.Among them,the construction of spin crossover complexes with significant hysteresis transition or near room temperature transition is of great significance for the development of bistable molecular magnetic materials with switching properties and memory conductivity.However,the directional design and property regulation of such complexes is still a difficult problem that has not been overcome.In this paper,a series of tetradentate nitrogen-containing heterocyclic compounds were designed and synthesized,and then the Fe(II)spin crossover complexes with ideal properties were constructed and characterized.The full text is divided into four chapters:In the first chapter,nitrogen-containing heterocyclic compounds and their applications are introduced.Then,the molecular magnetic materials,the concept and application of spin crossover complexes,and several research systems in which spin crossover can occur are introduced.Finally,the thesis expounds the idea of topic selection and research content.The second chapter is the synthesis process of tetradentate nitrogen-containing heterocyclic compounds.The preparation process and characterization of a series of tetradentate nitrogen-containing heterocyclic compounds(L_6Me,L_5Me,L_5Me-O,L_bz,L_cbzand L_jajer)are introduced.In the third chapter,the tetradentate nitrogen-containing heterocyclic compounds L_6Me,L_5Meand L_bzwith suitable field strength are selected as the main ligands.Eight new Fe(II)complexes were constructed:[Fe L_6Me(NCS)₂](1),[Fe L_6Me(NCSe)₂](2),[Fe L_6Me(NCBH₃)₂](3),[Fe L_5Me(NCS)₂](4),[Fe L_5Me(NCSe)₂](5),[Fe L_5Me(NCBH₃)₂](6),[Fe L_bz(NCS)₂](7)and[Fe L_bz(NCSe)₂](8).By single crystal X-ray diffraction analysed,the derivatives with the same main ligand were heterogeneous isomorphous structures.By magnetic susceptibility measurements analysed,complexes 1,2 and 3were in high spin state.Complexes 4,5 and 6 all had complete one-step spin crossover with transition temperatures of 193 K,226 K and 330 K,respectively.Complexes 7and 8 also had complete one-step spin crossover behavior.And complex 7 had a hysteresis width of 17 K(wherein T_1/2?=92 K and T_1/2?=75 K).The complex 8 had a higher spin conversion temperature T_1/2=194 K.Through the research of 18 which have been reported in the known literature related complexes[Fe L(NCE)₂](E=S,Se,BH₃)and 1-8 with similar structures,the relationship between the magnetism and the structure of this type of complex was proposed.When the crystal stacking is the same,the tetradentate nitrogen-containing heterocyclic compound with moderate ligand field strength are selected,and the complex T_1/2can be adjusted by replacing the auxiliary ligand NCE^-.It is of great significance to reasonably design and fine-tune the characteristics of new switchable materials.However,complexes 1,2 and 3 still can not change their spin crossover behavior by replacing the ancillary ligand NCE^-,indicating that the ligand L_6Mehad a significant steric hindrance effect.The fourth chapter is a brief summary and prospect of the above work.