Studies On The Structures And Magnetic Properties Of 3d-4f Complexes Based On Schiff Base Ligands

Magnetic materials play an important role and are closely related to people’s life.Under the information age,the traditional magnetic materials as information storage do not conform to the trend of miniaturization and high storage.The reason is that traditional magnetic materials are magnetized by long range ordered interactions between molecules to form magnetic domains for information storage.The high density of information storage will lead to the increase of magnetic material volume.Single molecule magnets（SMMs）can effectively solve this problem,which relies on the magnetic relaxation behavior of a single molecule.In studying the properties of SMMs,researchers focus on improving the effective energy barrier(U_eff).In the design and synthesis of SMMs,4f-SMMs with excellent performance can be prepared by utilizing the sizable large magnetic anisotropy and moment for rare earth ions,and 3d-4f-SMMs are also the focus of researchers.In this paper,we synthesized 11 complexes by using Schiff base ligands,which can be divided into three categories and four structures.The contents are as follows:In chapter 2,three complexes with the same structure[Ni₄Ln₄（L1）₆（L’）₂{（Py）₂C（OCH₃）O}₂（μ₃-CO₃）₂（CH₃OH）₂]·x CH₃OH·y H₂O（Ln=Dy（1）,x=2,y=3;Tb（2）,x=7,y=1;Y（3）,x=6,y=1）were prepared by using schiff base ligand H₂L1 and auxiliary ligand2,2’-Dipyridyl Ketone（DPK）.Their crystal structures were analyzed.In complex 1,metal core[Ni₄Dy₄]forms a Z topological structure,which consists of a[Ni₂Dy₂]butterfly unit and two[Ni Dy]units.The transformation of CO₂in air into CO₃^2-in solution is involved in coordination,and the existence of CO₃^2-ions is confirmed by IR spectra and valence bond calculation.There are two different coordination configurations of Dy ^Ⅲin complex 1.The coordination configuration of Dy1 is biaugmented trigonal prism(BTPR-8,C_2v),with CSh M=1.577.The coordination configuration of Dy2 is triangular dodecahedron(TDD-8,D_2d)with CSh M=2.836.Magnetic studies show that complex 1has the frequency and temperature dependence of out-of-phase（χ’）ac susceptibility signals（AC）,and the effective energy barrier(U_eff)is14.94（1）K.In chapter 3,six complexes containing[M₂Dy₂](M=Ni ^Ⅱ,Zn ^Ⅱ)with butterfly topologies were obtained by using Schiff base ligand H₂L1 and metal salt(3d=Ni ^Ⅱ,Zn ^Ⅱ;4f=Dy ^Ⅲ)in different solvent reaction,and molecular formula as follows:[M₂Dy₂（L1）₄（A）₂（B）₂]·x C·y D,(4,A=CH₃COO^-,B=DMF,x=0,y=0;5,A=CH₃COO^-,B=Me OH,C=Me OH,x=2,y=0;6,A=Cl^-,B=Me OH,x=0,y=0;7,A=NO₃^-,B=Me CN,C=Me CN,x=4,y=0;8,A=NO₃^-,B=DMF,C=DMF,D=H₂O,x=2,y=4;9,A=CH₃COO^-,B=DMF,C=Me OH,x=2,y=0;4-8,M=Ni ^Ⅱ;9,M=Zn ^Ⅱ).The coordination configuration of Dy in complexes 4-5 are the biaugmented trigonal prism(BTPR-8,C_2v),with CSh M value is 1.490 and 1.424,respectively.Complex 5 replaces DMF molecule in complex 4 with methanol molecule.The coordination configuration of Dy ^Ⅲin complex 6 is pentagonal bipyramid configuration(PBPY-7,D_5h),with CSh M=1.331.Coordination configurations of Dy ^Ⅲin complexes 7-8 are triangular dodecahedron(TDD-8,D_2d),with CSh M values is 2.905 and 1.223,respectively.The difference between complex8 and 4 is that CH3COO^-in 4 is replaced by NO₃^-in 8.The complex 9,which is a paramagnetic Ni ^Ⅱion of 4,is replaced by diamagnetic Zn ^Ⅱion,with the same Dy ^Ⅲcoordination configuration,with CSh M=1.427.Importantly,the easy magnetization axes of these complexes all point towards the O atom of phenoxido group in the ligand H₂L,and the molecules of these complexes can be replaced freely,thus regulating the Dy ^Ⅲcoordination configuration and the charge density distribution of the surrounding ligands.Magnetic measurements of complex 4 show that theχ’are frequency and temperature dependent,and the effective barrier is up to 407.7（1）K.In Chapter 4,two 4f complexes were synthesized.Complex 10belongs to a mononuclear Dy complex.The coordination configuration of Dy is spherical tricapped trigonal prism(TCTPR-9,D_3h),CSh M=1.096.The effective energy barrier of 11[Dy₂（L₂）₂（tfac）₂]was 234.8（3）K,and that of the magnetic dilution sample was 188.0（6）K.The effective energy barrier of the reported Dy₂-hfac（d）complex was 110 K.Through theoretical calculation,it is proved that the asymmetric ligand tfac regulates the interaction between Dy ^Ⅲion and ligand charge,that is,weak equatorial and/or strong axial interactions are helpful to increase the energy barrier.In addition,the interaction between Dy ^Ⅲions was antiferromagnetic,and there was a large exchange coupling parameter,resulting in an open hysteresis loop under zero field.The hysteresis loop of the complex 11@Y shows a butterfly shape,which was due to magnetic dilution and the weakening of antiferromagnetic coupling was not enough to suppress the QTM effect.