Synthesis And Characterization Of Divalent Ferromagnetic Complexes Based On Nitrogen Heterocyclic Ligands

As the whole society development of information technology,magnetic materials have become the research focus in many fields.At the same time,with the development of the times and technological innovation,people have higher and higher requirements for information storage materials.Lightweight,portable and high-density information storage has been the goal of many researchers.In the past few decades,transition metal based complex magnetic materials have become a new favorite in this field.This is due to the relatively simple electronic structure of molecular based magnetic materials,which can change the coordination number,coordination range and structural deformation according to the needs of use.Molecular based magnetic materials are synthesized by supramolecular self-assembly method,which can construct nanostructures from molecules or even atoms.It can not only meet the requirements of small size and perfect unity of properties,but also enable us to study the relationship between magnetism and structure through their determined crystallographic structure.With the change of the coordination number of the central metal ions and the different coordination atoms,the ligand field strength will change,which will have a significant impact on the properties of magnetic materials.These problems lead to the design and synthesis of molecular based magnetic materials with special properties is still a great challenge in molecular magnetism and materials science.Molecular-based magnetic materials can be roughly divided into single-molecule magnets,single-stranded magnets and other molecular nano-magnets and magnetic bistable materials.Among them,spin-crossing complexes are the most widely studied in sub-bistable materials.This article uses different synthesis methods and crystallization methods to design molecular-based materials.At the same time,the crystal structure,magnetic properties of the synthesized materials were further characterized and studied.The main researches are listed as follows:The first chapter,the introduction part,introduces the spin-crossover phenomenon,the characterization methods and synthesis strategies of spin-crossover complexes,focusing on the research progress of spin-crossover complexes of different dimensions,and the factors that affect the properties of spin-crossover.In addition,the research ideas of this article and the significance of topic selection are also explained.Chapter two,usingthebidentatepyridineligand N,N'-bis-(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide(dpni)and Fe(Cl O₄)₂·9H₂O and K[Au(CN)₂],designed and synthesized a new type of three-dimensional Hoffman-type compound[Fe(dpni){Au(CN)₂}₂]·4CH₃CN(1)by a liquid-liquid slow diffusion method at room temperature.The complex exhibits one-step incomplete spin crossover behavior.The reversible change between the incomplete spin crossover property and the non spin crossover property is related to the desorption and reabsorption of acetonitrile solvent molecules.In complex 1,the guest molecules play a key role in regulating the spin crossover properties.The weak intermolecular hydrogen bond interaction(C-H…O)between acetonitrile and the complex framework is an important factor in regulating the spin crossover properties of complex 1.Because of these properties,complex 1 can be a new type of molecular switch material.Chapter three,monodentate pyridine ligands isoquinoline(isoq),Fe SO₄·7H₂O and K₂[Pt(CN)₄](K₂[Ni(CN)₄])by a liquid-liquid slow diffusion method at room temperature was designed and synthesized two new two-dimensional Hoffman-type compounds{Fe(isoq)₂[Pt(CN)₄]}(2)and{Fe(isoq)₂[Ni(CN)₄]}(3).Complex 2 exhibits a one-step complete spin crossover with a hysteresis loop of 25 K.The complex can be used as a new type of chemical sensor material.Complex 3 is paramagnetic in the temperature range of2-300 K,without spin crossover.In chapter four,two novel zero-dimensional mononuclear compounds[Fe(TBZ)(HTBZ)₂]Cl O₄(4)and[Fe(TBZ)₂SO₄H₂O](5)were designed and synthesized by hydrothermal method with bidentate benzimidazole ligand 2-(4-thiazolyl)benzimidazole and Fe(Cl O₄)₂·9H₂O,Fe SO₄·7H₂O.Complex 4 is paramagnetic in the temperature range of 2-300K,without spin crossover.Chapter five,summary and outlook.