Synthesis And Magnetic Properties Of Single Ion Magnets Of Mn(Ⅱ)-Containing Complexes With High Coordination Number

The design and synthesis of single-molecule magnets（SMMs）with potential applications in ultrahigh density memory components,spintronic devices and processing technologies has attracted wide attention over the last two decades.There is a growing interest on designing mononuclear SMMs based on first-row transition metal ions,because they have exhibited a rising trend to compete with the well-developed lanthanide-based SMMs.In this paper,a series of high-coordinated Mn（Ⅱ）and Co（Ⅱ）complexes have been designed and synthesized,and their crystal structures have been determined by X-ray crystallography and their magnetic properties have been investigated.Thus,the magnetic structure relationship has been studied in depth.The main works of this paper are as follows:In chapter one,the basic concepts,detection methods and research advances of single molecular magnet were introduced.In chapter two,four mononuclear 7-coordinate compounds,[Mn^Ⅱ（L¹）（H₂O）₃]（1）,[Mn^Ⅱ（L²）（H₂O）₃]（2）,[Mn^Ⅱ（L³）（H₂O）₂（CH₃CH₂OH）]（3）and[Co^Ⅱ（L¹）（H₂O）₃]（4）have been obtained via the hydrothermal reactions of tetradentate ligands H₂L¹（1,10-phenanthroline-2,9-dicarboxylic acid）,H₂L²（2,2’-bipyridine-6,6’-dicarboxylic acid）and H₂L³（6,6’-bis（1H-tetrazol-5-yl）-2,2’-bipyridine）with hydrated Mn（Cl O₄）₂ and hydrated Co（NO₃）₂.These compounds have been well characterized by IR,elemental analysis,and their structures have further determined by X-ray crystallography.Their magnetic properties have been investigated under a external dc field.The crystal structures clearly show that all the metal centers in thesecomplexes are 7-coordinated by a tetradentate ligand and three solvent molecules in a pentagonal bipyramid.Through magnetic measurements,all compounds show interesting slow magnetic relaxation under an external direct current（dc）field.Most interestingly,all compounds show dual relaxation processes.In chapter three,four 8-coordinate Mn（Ⅱ）compounds,[Mn^Ⅱ（Lⁿ）₂]（Cl O₄）₂（5-8）have been obtained from the reactions of four neutral tetradentate ligands,2,9-bis（carbomethoxy）-1,10-phenanthroline（L⁴）,2,9-bis（carbomethoxy）-2,2′-dipyridine（L⁵）,N²,N⁹-dibutyl-1,10-phenanthroline-2,9-dicarboxamide（L⁶）,6,6′-bis（2-（tert-butyl）-2H-tetrazol-5-yl）-2,2′-bipyridine（L⁷）with hydrated Mn^Ⅱ（Cl O₄）₂.These compounds have been characterized by UV/vis,IR,MS,elemental analysis,X-ray crystallography and magnetic measurement.The crystal structures have exhibited that these four complexes are 8-coordinated in the distorted triangular dodecahedrons.All of these Mn（Ⅱ）compounds show interesting slow magnetic relaxation behaviors under an applied direct current field.Structurally,5 and 6 have a nearly identical 8-coordinate environment and accordingly,5 and 6 exhibit similar magnetic relaxation behaviors.8 has weak ferromagnetic coupling.Due to the amide O atoms are stronger donors,the relaxation process of 7 is much more complicated.The magnetic properties of these Mn（Ⅱ）compounds are also significantly affected by slight variation of ligands.This is the first report about 8-coordinated Mn（Ⅱ）single ion magnet.In chapter four,the work of this paper is summarized,and more ideas are provided for exploring the magnetic structure relationship of single molecule magnet.