Synthesis,Crystal Structure And Magnetic Regulation Of Complexes Containing Rare Earth Metals

In the past few years,single-molecule magnets?SMMs?have experienced great development in the field of molecular-based magnetic materials due to the slow relaxation of single-molecule magnets and the potential applications in the field of high-density information storage and quantum computation.At present,most efforts have been made to explore the main factors that influencing the energy barrier and the magnetic blocking temperature.To this end,4f rare earth metal having a large anisotropy and 3d transition metal having a large ground state spin are combined to synthesize excellent performance metal complex.However,the fast magnetization quantum tunneling effect?QTM?still exists for latest lanthanide single-molecule magnets under zero applied fields,which often affects the height of energy barrier and the length of relaxation time.Up to now,QTM has become the biggest obstacle to synthesis single-molecule magnets with better performance.There are two main methods to suppress QTM:one is to improve the symmetry of the metal center in the lanthanide system;the other is to enhance the magnetic exchange of the metal center.The synthesis of 3d-4f SMMs provides a new strategy for researchers and impels people to explore the synthesis of excellent properties of SMMs.In this paper,we primitively introduce about single molecule magnets and summarize the research progress of SMMs of several 3d-4f reported in recent years;meanwhile,we have prepared and characterized some 3d-4f SMMs.The main contents are as follows:The first chapter is the introduction.This chapter mainly introduces the research background of single-molecule magnets,including the research method and development bottleneck.Next gives a brief description of several kinds of 3d-4f single-molecule magnets which have been synthesized in recent years.Finally,we put forward the significance and innovation of this paper.The second chapter is to study the structure and properties of the synthesized five Zn-Ln metal complexes.Compound Zn₄Ln₂?Ln=Dy 1,Tb 2,Gd 3,Ho 4?is a homologue.It is worth noting that multidentate organic ligands formed by absorption CO₂in air through in-situ reactions and participates in the coordination in the process of synthesis for compounds 1-4.Compound 1 differs from compound 2-4 about the peripheral neutralization ions in the structure,there is a symmetric disordered[Zn N₃Cl₃]^2-unit for compound 2-4 and two Cl^-ions for compound 1,respectively.The magnetic measurement of the compounds1-3 was carried out,and the energy barrier of the compounds 1 and 2were fitted to be 30.66 K and 8.87 K under different applied fields using the Arrhenius law[?=?₀exp(U_eff/k T)],but considering the multi-relaxation process?^-1=?_QTM^-1+CTⁿ+?₀^-1exp(-U_eff/k _BT),the energy barriers of compounds 1 and 2 are 22.4 K and 2.4 K,respectively.The magnetic measurement for compound 3 shows that the Gd ions have weak antiferromagnetic interaction.The energy barriers(U_cal)can be estimated to be 93.4 cm^-1and 177.4 cm^-1by the complete-active-space self-consistent field?CASSCF?calculations,for 1 and 2,respectively,which are much higher than the values of the estimated U_eff(U_eff=30.66K for 1 and 8.87 K for 2),and analyzed the reasons.The total coupling constant(J_total=J_dip+J_exch)was introduced by calculating,and concluded that total coupling constant of compound 1 and 2 is antiferromagnetic and ferromagnetic,respectively.At the same time,the main magnetic axis direction of compounds 1 and 2 is calculated to point to Dy1-O5 and Tb1-O6,respectively,and the reason why the main magnetic axis direction of the two compounds is different is also analyzed.Compound 5is a Zn₂Dy₂structure and there are two mixed ligands involved in the coordination process,which enriches the Zn-Ln metal cluster system.The third chapter is about the characterization and study of three Fe-Ln metal clusters.In this chapter,a series of Fe ₂^?Ln₂metal clusters?Ln=Dy 6,Tb 7,Gd 8?were synthesized by using mixed ligands of polydentate Schiff base and triethanolamine.The magnetic analysis of compound 6 shows that frequency-dependent out-of-phase susceptibility??_M??signals were observed and no obvious peaks whether there is an external magnetic field or not,which indicates that compound 6 has the single-molecule magnets behavior.Therefore,the formula ln??_M?/?_M??=ln???₀?+E_a/k _BT,is used to calculate the average energy barrier of compound 6 is 6.86 K,?₀=3.92×10^-7s.In fourth chapter,four Co ₂^?Ln₂complex?Ln=Dy 9,Tb 10,Ho 11,Gd 12,?and a Co₂Na?compound 13?metal cluster were synthesized and analyzed.In the synthesis of Co ₂^?Ln₂metal complex,the mixed ligands of polydentate Schiff base ligand and rigid ligand 2,6-pyridyl-dimethyl alcohol were used.The?_M?susceptibilities clearly show temperature-and frequency-dependent signal for complex 9,showing that complex 9possess SMMs behavior.For complex 9,a thermally activated anisotropy barrier is 46.42 K in zero dc applied field and 63.95 K in 2000 Oe dc field.However,the formula?^-1=?_QTM^-1+CTⁿ+?₀^-1exp(-U_eff/k _BT)is used to consider multi-relaxation process,the effective energy barrier for compound 9 is 40.09 K in zero dc applied field and 47.86 K in 2000 Oe dc field.Compound 13 is a heteronuclear Co₂Na compound.In the synthesis of complex 13,4f metal is not involved in coordination although 4f rare earth salt is added,but 3p metal Na is involved in coordination.