| Molecular-based magnets have potential applications in high-density information storage,molecular spintronics,and quantum computing.Among them,the research on the construction and performance of Ln-single-molecule magnets(Ln-SMM)is the current research focus of molecular magnetism.This work aims to explore the factors of the magnetic relaxation dynamics of Ln-SMM,and to provide a synthesis strategy and theoretical basis for the design and synthesis of single-molecule magnets with high energy barriers and high blocking temperatures.Herein,Dy(III)is selected as the paramagnetic center,and[DyN2O6]mononuclear complexes are constructed by combining ?-diketone ligands and auxiliary ligands of the bidentate chelate coordination mode.The resulting complexes have been structurally and magnetically characterized,of which the magneto-structural correlations have been studied by the combination of experiments and theoretical calculations.In addition,the tridentate acylhydrazone ligand was selected as the main ligand of the fixed structure,and four new mononuclear complexes were synthesized by means of the control of solvent effects and the introduction of different ?-diketone ligand.Intensive research on magnetic structure relations.The contents and conclusions are as follows:1.A series of mononuclear ?-diketonate-Dy complexes,with formulas[Dy(tmhd)3(X)][5,5-(CH3)2-bpy(1),4,4-(CH3)2-bpy(2),4,4-((CH3)3)2-bpy(3),4,4-(OCH3)2-bpy(4)],(tmhd=2,2,6,6-tetramethyl-3,5-heptanedione,5,5-(CH3)2-bpy=5,5'-di-methyl-2,2'-bipyridine,4,4-(CH3)2-bpy=4,4'-di-methyl-2,2'-bipyridin,4,4-((CH3)3)2-bpy=4,4'-di-tert-butyl-2,2'-bipyridin,4,4-(OCH3)2-bpy=4,4'-di-methoxy-2,2'-bipyridin),have been prepared by altering the capping N-donor coligands.Dy(?)ions in all complexes exhibit the N2O6 octa-coordinated sphere with a distorted square-antiprism(D4d).Magnetic studies reveal a SMM behavior in all complexes with the energy barriers of 38.68 K(1),213.85 K(2),202.23 K(3)and 216.10 K(4)in zero field,as well as 161.3 K(1),232.2 K(2),271.05 K(3)and 264.64 K(4)under a static field.Although the high symmetric geometry(D4d)has been observed in all cases,the different natures of the N-donor ligands induce changes on the coordination microenvironment,giving rise to distinct dynamic magnetic behaviors.2.By means of the facile chemistry,structural assembly,and transformation of four mononuclear Dy(?)complexes,Dy(bpad)3·CH3OH·H2O(9),Dy(bpad)2(H2O)2·NO3(10),[Dy(bpad)2(tmhd)](11),and[Dy(bpad)2(btfa)](12)(Hbpad=N3-benzoylpyridine-2-carboxamidrazone,tmhd=2,2,6,6-tetramethylheptane-3,5-dione,btfa=3-benzoyl-1,1,1-trifluoroacetone),with distinct architectures and local symmetries were established.The disparity of the coordination geometries around the Dy(?)ion among these complexes impacts the strength of the crystal field and the local tensor of anisotropy(D)of each Dy site and their relative orientations,therefore giving rise to diverse SMM behaviors with distinguishing relaxation energy barriers of 106.93 K for 9,52.55 K for 10,48.16 K for 11 and 51.41 K for 12.The differences of the magnetic property and the magnetic anisotropy for four complexes have been explained by ab initio calculations,which are corresponding to the experimental results. |
PDF Full Text Request