Magneto-Structural Correlations In Polynuclear Dysprosium(?) Single-Molecule Magnets

In recent years,lanthanide single molecule magnets(SMMs),especially dysprosium-based single molecule magnets,as a remarkable class of molecular magnetism,have attracted more attention from scientists.Compared with traditional bulk magnets,the molecular nature of SMMs offers unique properties,which has great application prospect in molecular spintronics,ultra-high density information storage and quantum bit processing.Based on the design,synthesis and magnetic properties of polynuclear dysprosium SMMs,we employed a series of tridentate Schiff base ligands as the key ligands for fixing the structural framework as well as DMF,DMA etc.as the auxiliary ligand for fine-tuning the coordination geometry of dysprosium ion to construct ten polynuclear Dy(?)complexes,and the magneto-structural correlations of these complexes are depth investigated deeply.Six chapters are included in the dissertation:In Chapter 1,the development,origin and application of magnetism were introduced firstly.Then,the research background,theoretical basis,as well as the research progress of SMMs were described.Finally,the general ideas and the current progresses of the whole dissertation were briefly accounted.In Chapter 2,with the purpose of constructing high-performance polynuclear dysprosium SMMs,CO2 was captured from atmosphere under ambient conditions for reducing and sequestering into a novel high-performance polynuclear Dy(III)SMMs[Dy2(L)2(DBM)2(DMF)2](HDBM = dibenzoylmethane)through an in situ organic ligand reaction of hydrazine.In this in situ reaction,a new ligand(H2L = 2-(2-hydroxy-3-methoxybenzylidene)hydrazine-1-carboxylic acid)is observed and the reasonable reaction mechanism is proposed by comparable crystal structure([Dy2(L)2(DBM)2(DMA)2])and synthesis experiments(in presence or absence of CO2).Importantly,the improvement of SMMs properties in these two complexes caused by the modification of the axial ligand also provided a guideline to design and synthesize the high-performance polynuclear Dy(III)based SMMs.In Chapter 3,the strategy for enhancing SMMs properties founded in the previous chapter were verified experimentally and its theoretical basis was explored.By employing 2-hydroxy-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide(H2L)as the periphery ligand,two dinuclear complex Dy2(L)2(DBM)2(DMF)2]and[Dy2(L)2(DBM)2(DMA)2]·2DMA were constructed.Similarly,by replacing the DMF(dimethylformamide)ligand with DMA(dimethylacetamide)while retaining the same coordination atoms,the significant improvement of SMMs properties was achieved.Ab iniitio calculations revealed that the increasement of average charges along the magnetic axes is the key factor to determine the improvement of SMMs properties,which presents a simple method to rationally improve relaxation properties for the polynuclear Dy(III)based SMMs.In Chapter 4,the transitions of two magnetic interaction states(antiferromagnetic or ferromagnetic)upon structural variations in polynuclear Dy(III)complexes was investigated.Two dinuclear dysprosium complexes,namely[Dy2(L)2(DBM)2(DMA)2]·2DMA.2CH3CN and Dy2(L)2(DBM)2(DMF)2](H2L = 2-(2-hydroxy-3-methoxybenzylideneamino)phenol),are introduced.Slightly changes in the Dy-O-Dy angle and Dy…Dy distance in the ?Dy2O2?core of the two complexes can cause the transition between antiferromagnetic and ferromagnetic interaction.As demonstrated using ab initio calculations,the transition between two magnetic interaction states(antiferromagnetic or ferromagnetic)is a result of the different sensitivities of the dipolar interaction and the exchange interaction between the Dy(III)ions to the structural variations.In addtion,the ferromagnetic complex possessed better SMMs proformance than antiferromagnetic one.This work also provided a guideline to regulate the magnetic interaction and relaxation properties for polynuclear Dy(III)based SMMs.In Chapter 5,how to regulate the magnetic interaction and relaxation properties in higher nuclear system,tetranuclear dysprosium SMMs was investigated.Method based on electrospray ionization mass spectrometry(ESI-MS)and X-ray crystallography diffraction in combination was employed to elucidate the formation process of tetranuclear dysprosium system and determine the accurate position of its changeable coordination site.Then,armed with strategies about improving relaxation properties and the transitions of two magnetic interaction states upon structural variations,the condensed phase synthesis with improved relaxation properties and desired magnetic interaction state was achieved through targeted fine-tuning the coordination geometry of the site.Finially,the goal of the function-oriented regulation of magnetic behaviors of polynuclear Dy(III)SMMs was achieved.In Chapter 6,briefly conclusions to the whole work.