The Design,Synthesis And Characterization Of Tetranuclear Magnetic Function-Derected Lanthanide-based Complexes

In recent years,the study of functional rare earth complexes have been one of the research hotpots for scientists,and researches on single-molecule magnet（SMM）and molecular magnetic refrigeration materials have been one of the important works in this field.In this thesis,we summarized the published works on single-molecule magnet,molecular magnetic refrigeration,8-hydroxyquinoline derivatives andβ-diketones.Taking advantage of above results,ten lanthanide complexes based on8-hydroxyquinoline Schiff Base derivatives andβ-diketones coligands were synthesized.The complexes have been characterized by X-ray single crystal diffraction,EA,X-ray power diffraction,TG,IR,UV.The magnetic properties of some complexes have been investigated.The main contributions in this dissertation are as below:1.Two 8-hydroxyquinoline Schiff base derivatives（HL1 and HL2,HL1=5-（benzylidene）amino-8-hydroxylquinoline and HL2=5-（4-pyridinecarboxaldehyde）amino-8-hydroxylquinoline）were synthesized in a simple condensation reaction of5-amino-8-hydroxylquinoline with benzaldehyde and 4-pyridinecarboxaldehyde,respectively.2.Five new tetranuclear complexes based on 5-（benzylidene）amino-8-hydroxylq--uinoline（HL1）andβ-diketone coligand acetylacetonate（acac）,[Ln₄（acac）₄（L1）₆（μ₃-OH）₂]?CH₃CN?0.5CH₂Cl₂（Ln=Gd（1）,Tb（2）,Dy（3）,Ho（4）and Er（5））have been synthesized,structurally and magnetically characterized.Complexes 1-5 have similar tetranuclear structures.Each Ln^Ⅲion is eight coordinated and their coordination polyhedrons can be described as being in a distorted square-antiprismatic geometry.The magnetic studies reveal that 1 features magnetocaloric effect（MCE）with the magnetic entropy change of-?S_m（T）=25.08 J kg^-11 K^-11 at 2 K for?H=7 T,and 3displays slow magnetic relaxation behavior of Single Molecule Magnets（SMMs）with the anisotropic barrier of 86.20 K and pre-exponential factorτ₀=2.99×10^-88 s.3.Five tetranuclear lanthanide complexes with formulas[Gd₄（dbm）₄（L2）₆（μ₃-OH）₂]·5CH₃CN（6）,[Tb₄（dbm）₄（L2）₆（μ₃-OH）₂]·2CH₃CH₂OH·4CH₃CN（7）,[Dy₄（dbm）₄（L2）₆（μ₃-OH）₂]·4CH₃CN·2H₂O（8）,[Ho₄（dbm）₄（L2）₆（μ₃-OH）₂]·CH₃CH₂OH·4CH₃C N·2H₂O（9）,[Er₄（dbm）₄（L2）₆（μ₃-OH）₂]（10）,were obtained from the reaction of5-（4-pyridinecarboxaldehyde）amino-8-hydroxylquinoline（HL2）and Ln（dbm）₃·2H₂O（dbm=1,3-diphenyl-1,3-propanedione）.X-ray crystallographic analyses reveal that6-10 have similar tetranuclear structures.Each Ln^IIIII ion is eight coordinated and their coordination polyhedrons can be described as being in a distorted square-antiprismatic geometry.Magnetic studies indicate that complex 6 features magnetocaloric effect（MCE）with the magnetic entropy change of-?Sm（T）=16.35 J kg^-11 K^-11 at 3 K for?H=7 T;and complex 8 displays single-molecule magnet behavior,exhibiting an effective energy barrier of the relaxation of the magnetization U_eff/k_B=89.38 K and the pre-exponential factorτ₀=3.32×10^-88 s.