Magnetic Properties Of Rare Earth Metal Complexes With Mixed Mutidentate Ligands

Magnetic materials have attracted an increasingly wide attention in modern science and technologies,and people have put forward the more and more high requirements to the materials.However,the traditional magnetic materials have more limited information storage capacity,so the single molecule magnets?SMMs?came into being.The magnetism of SMMs comes from single molecule,and it can exhibit slow relaxation of the magnetization below a blocking temperature?T_B?.It have the advantages of small size,easy dissolution,good dispersibility,and easy processing,which makes it have broad application prospects in quantum computation,high-density information storage,molecular spin and magnetic refrigeration.3d-SMMs and 3d-4f SMMs have always been a hotspot in the study.However,it is found that the 3d orbitals of 3d mental ions will be quenched under the ligand field,resulted the small spin-orbit coupling effects,that is,it is hard to improve spin?S?and negative uniaxial anisotropy?D?at the same time.The introduction of 4f mental ions can increases the anistropic parameters,but the magnetic coupling in 3d-4f SMMs is relatively small,which results the effective barrier(U_eff)between the ground state and the excited state was difficult enhanced.Therefore,our research object is the structure and magnetic properties of 4f-SMMs.The 4f mental ions will not be quenched in the crystal field,and it can produce stronger spin-orbital coupling and large magnetic anisotropy.Using two kinds of chelate ligand with different symmetry and coordination properties synthesized 4f mental complexes containing such topological structures as linear,triangular and quadrangle cones,it is propitious to unify the direction of magnetic anisotropy axis,at the same,chelating ligands with high symmetry are choosed to increase the symmetry of 4f mental ions within complexes.Thus,4f SMMs with high energy barrier and large blocking temperatures may be obtained.The main contents of this paper are summarized as follows:Chapter one mainly introduces the background and development of SMMs,including the research significance and research methods and the different types of SMMs,and puts forward our highlights of innovation and research thoughts.In the second chapter,the structures and magnetic properties of eight 4f rare earth metal complexes were studied and analyzed.Compounds 1-3 consist of Dy₉,Ho₉ and Er₉ units,respectively,and the ac magnetic susceptibility measurements of compound 1 shows the frequency dependence of the out-of-phase signals for 1,which indicates that 1 exhibit single molecular magnet behavior.Compound 4 is irregular tetrahedron Dy₄ complex;the measurement of ac magnetic susceptibility shows that 4also shown single molecular magnet behavior.Moreover,the U_eff=15.60 K,?₀=2.25×10^-6 s at high temperature is obtained by fitting the ac data.Compound 5 is“Z”-like Dy₄ complex.Both 5 and 6 are Dy-Na complexes,and the frequency-dependent signals appear from their ac susceptibilities,and observed obvious peaks of compound 6,indicating that both 6 and 7 show the single molecule magnet behavior.For compound 6,the effective energy barrier and?₀ are 13.21 K and3.94×10^-6 s,respectively.Compound 8 bridged both L₁ and trifluoroacetylacetone ligands,and the temperature-and frequency-dependent ac magnetic susceptibility were observed with good peaks,indicating that 8 process single molecule magnetic behaviour with U_eff=129.8 K and?₀=2.18×10^-8 s.In the third chapter,we studied the structures and magnetic properties of one Cu₄?9?compounds and a series of Cu3Ln2?10-14?complexes.The compounds 10-14contains ring-like[Cu₃Ln₂]metal centers,in which compounds 10[Cu₃Ho₂]and 13[Cu₃Er₂]are one-dimensional chain structure connected by N₃^?.The measurement of the ac susceptibilities for compound 10 showed the behavior of single molecule magnets,but the peaks was not observed,with U_eff=16.67 K and?₀=8.79×10^-6 s under a 1000 Oe field by employing the method of Bartolomé.