Polyol Compound As Ligand:Synthesis,Self-assembly And Magnetic Characterization Of High Spin Mn Clusters

Polynuclear manganese clusters have received considerable attention in recent years for their potential application as single molecule magnets,spintronic devices,molecular nanomagnets for magnetic cooling,molecular nanomagnets for quantum information processing and relevance to bioinorganic chemistry.A distinct metalloenzyme in nature is the oxygen-evolving complex(OEC)in photosystem Ⅱ(PS Ⅱ)of green plants,which contains a Mn4CaOx active site.The aim of this dissertation is to synthesize high-spin manganese clusters with single molecule magnets characteristics and explore the new methods that can be used to synthesize designed structure effectively and control the magnetic properties of clusters.In the first chapter of this dissertation,we mainly reviewed the development of single molecule magnet,single chain magnet and single ion magnet.A short account of the research background and purposes is also given.Single-molecule magnets can be defined by being magnetized under an applied magnetic field below the blocking temperature;there is still remanence after the removal of applied magnetic field;it is caused by single molecule itself,namely spin values and anisotropies of molecule,which is different from intermolecular interactions or long-range ordering.Single-molecule magnets can be view as magnetic compounds made up of metal ions binding through organic ligands.The magnetism derives from the magnetic coupling between metal centers with unpaired electrons.Due to the diversity and variability of organic structures,the structure of the clusters can be modified by changing the organic ligands to achieve the control of molecular magnetism.Based on the above advantages,Single-molecule magnets would exhibit more magnetic properties than conventional magnetic materials.How to design and synthesize the designed structure is a hot topic in the research of manganese clusters.Manganese element has been drawn a great deal of attention for the large number of unpaired electrons in the outer layer,the strong Jahn-Teller effect of MnⅢ and the variety of atom valence.However,the Mn-O-Mn bond angle and the Mn-Mn distance within a certain range are necessary for the ferromagnetic interaction between manganese atoms which brings difficulty to directional synthesis.Therefore,the "building block" approach is an efficient way to obtain new types of manganese clusters.This approach is achieved by self-assembly of "building block" through stepwise reaction.The "building block" unit needs to qualify three conditions:1)"building block" must be relative stability or can be generated preferentially in the reaction and occupy a dominant position in quantity.2)Uncoordinated sites of"building block" are active to sustain the reaction.3)Magnetic properties of "building block" can be sustained,which requires the chemical structure of the building block being sufficiently stable during the self-assembly process or magnetic properties can be tolerant to structural changes.However,the coordination modes of a given ligand and the resulting cluster topologies are relatively limited,which somewhat restricts the discovery of new clusters with new structures and novel magnetic properties.Consequently,in order to promote the progress of manganese aggregates,developing new ligand system is among the most prominent solutions.An alternative approach is to covalently integrate two or more present chelating/bridging ligand to form a new"merged-ligand".The origin of "merged-ligand" is to utilize the known ligands and their relatively fixed metal coordination modes to build new metal clusters.Compared to conventional method of mixing various kinds of ligands and different types of metal ions randomly,the employment of merged ligand leads to synthesize the complexs in a certain direction.The synthesis of functionalized high spin manganese clusters is also one of the focused research topics in this dissertation.In recent years,the Aggregation Induced Emission(AIE)phenomenon has attracted the attention of researchers.The molecules with AIE characteristics would obtain good luminescence property for the molecular configuration being limited in crystal material due to the intermolecular stacking.Therefore,it is of great significance to study the high spin manganese clusters based on ligands containing AIE motif.In the second chapter of this dissertation,we found that the linear MnⅡ-MnⅢ-MnⅡbasic structure chelated by 1,3-propanediol ligands is a good building block through the summary of reported literatures and the previous works by our group.Within the motify of 1,3-propanediol ligand,2-amino-1,3-propanediol would retain the coordination mode of 1,3-propanediol ligand.It would be a good research system for the amino can be modified in various ways by simple organic reactions to achieve the control of structure and magnetism.We obtained 5 kinds of serinol derivative organic ligands(H2L1-H2L5)by modifying different substituents on serinol.Seven metal manganese clusters were obtained by different synthesis methods,namely[MnⅢMnⅡ2(HL1)2Br3(MeOH)6]·Br2(1),[MnⅡ6MnⅢ4(HL1)4(μ4-O)4(PhCOO)12]·(MeOH)(2),[MnⅡ6MnⅢ4(HL2)4(μ4-O)4(PhCOO)12](3),[MnⅡ4MnⅢ2(L2)4(PhCOO)6(MeOH)2](4),[MnⅡ6MnⅢ4(HL3)4(μ4-O)4(PhCOO)12](5),[MnⅡ6MnⅢ4(HL4)4(μ4-O)4(PhCOO)12](6),[MnⅢ4MnⅡ6(L4)2(L5)6(PhCOO)8(MeOH)4]·(MeOH)2(7).The author investigated the crystal structure,the magnetic properties and influence of structure on magnetic properties.In the third chapter of this paper,we synthesized 5 kinds of novel ligands H2L6-HxL10(x=3-4)containing hmp motif with different quantity of hydroxyl groups by applying aldol reaction.Seven metal manganese clusters were obtained by different synthesis methods,namely[MnⅢ2(L6)2(AcAc)2](8),[MnⅢ3MnⅡ(L6)6(Na)1.5(OH)0.5]·(MeOH)1.5(9),[MnⅢ2MnⅡ2(L6)4Br2(MeOH)2](10),[MnⅢ3MnⅡ(HL7)6]·(Me3NH)(11),[MnⅢ2(HL8)2(AcAc)2](12),[MnⅢMnⅡ2(HL9)2(MeCN)4(MeOH)Br2]Br(13),[MnⅢ2MnⅡ2(HL9)(L9)2(PhCOO)2(MeOH)(H2O)](14).The author investigated the crystal structure,the magnetic properties and influence of structure on magnetic properties.In the fourth chapter of this dissertation,we synthesized a novel ligand H3L11 with Aggregation Induced Emission(AIE)phenomenon.Three metal manganese clusters were obtained by different synthesis methods,namely[MnⅢMnⅡ2(H2L11)2(Cl)2(p-Toluic)2(MeOH)4]· Cl(15),[MnⅢMnⅡ2(H2L11)2(Br)5(MeOH)4]·(MeOH)2(16),[MnⅢ2MnⅡ2(HL11)2(p-Toluic)4(μ2-OMe)2(MeOH)2](17).The author investigated the crystal structure,the magnetic properties,the fluorescence properties and influence of structure on magnetic properties.In the fifth chapter of this dissertation,the above chapters are briefly reviewed and summarized.