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 and?-diketones.Taking advantage of above results,ten lanthanide complexes based on8-hydroxyquinoline Schiff Base derivatives and?-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?and?-diketone coligand acetylacetonate?acac?,[Ln₄?acac?₄?L1?₆??₃-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^?ion 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 factor?₀=2.99×10^-88 s.3.Five tetranuclear lanthanide complexes with formulas[Gd₄?dbm?₄?L2?₆??₃-OH?₂]·5CH₃CN?6?,[Tb₄?dbm?₄?L2?₆??₃-OH?₂]·2CH₃CH₂OH·4CH₃CN?7?,[Dy₄?dbm?₄?L2?₆??₃-OH?₂]·4CH₃CN·2H₂O?8?,[Ho₄?dbm?₄?L2?₆??₃-OH?₂]·CH₃CH₂OH·4CH₃C N·2H₂O?9?,[Er₄?dbm?₄?L2?₆??₃-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 factor?₀=3.32×10^-88 s.