The Application Of Metallocyanate(Cr,Fe,Co) Precursors In 3d-4f System Assembly And Their Effect On Magnetic Relaxation Properties Of Rare Earth Ions

With the in-depth study of various single-molecule magnets with novel structures,the rare earth ions(Dy^?,Ho^?,and Er^?)with large spin ground states and intrinsic magnetic anisotropy have become ideal central ions for the construction of SMMs and SIMs.In this thesis,organic ligands with larger steric hindrance and transition metallocyanate with higher symmetry are selected to regulate the coordination geometry of rare earth ions,and to explore the effect of the local geometric structure on the magnetic relaxation in the 3d-4f system based on transition metallocyanate.The main contents of this paper are as follows:1.Five cyano-bridged one-dimensional chain compounds with locally pentagonal bipyramid structure were synthesized using[TM(CN)₆]^3-(TM=Fe,Co)as bridging ligands and 2-Picoline N-oxide as auxiliary ligands with rare earth ions(RE=Y^?,Dy^?,Er^?).Thermal stability and magnetic properties of compounds 1YFe-5ErCo were tested.The results showed that compounds 1YFe-5ErCo had good thermal stability,and the magnetic results showed that 1YFe had paramagnetism.When a 1 kOe DC field was applied,compounds 2DyFe-5ErCo showed obvious magnetic relaxation behavior.Er analogues have better magnetic relaxation behavior than Dy analogues,and the QTM effect in RECo is weaker than that of REFe compounds.The crystal field formed by axially-elongated pentagonal-bipyramidal geometry is more favorable for Er^? than Dy^? ions to exhibit strong uniaxial magnetic anisotropy and SIM properties in these compounds.2.Six 3d-4f ion-pair compounds{[RE(4-MMNO)₂(H₂O)₅][Cr(CN)₆]}with locally pentagonal bipyramid structure were synthesized using [Cr(CN)₆]^3-as the counterion and 4-Methylmorpholine N-oxide as the auxiliary ligand with rare earth ions(RE=Y^?,Sm^?,Tb^?,Dy^?,Ho^?,Er^?).The thermal stability and magnetic properties of compounds 7SmCr?9DyCr and 10HoCr were tested.The results show that the compound has good thermal stability,magnetic studies have shown that this local high symmetry makes the central Ho^?ions exhibit Ising-like anisotropic.The AC susceptibility of 10HoCr in zero DC field and an applied 2 kOe DC field shows strong frequency dependence and SIM characteristics.The tailing phenomenon at low temperature may be due to the fact that Cr^?ions provide a strong transversal fluctuating field around the Ho^?ions,which leads to the rapid magnetic relaxation process of quantum tunneling.3.Three cyano-bridged 3d-4f compounds with local triangular dodecahedral structure were synthesized using[Cr(CN)₆]^3-as bridging ligands and Pyridine N-oxide or Propyleneurea or N,N'-Dimethylpropyleneurea auxillary ligands coordinated with Dy^? ions.Thermal stability and magnetic properties of compound 12DyCr-14DyCr were tested.The results showed that these compounds have good thermal stability.The magnetic results show that compounds 12DyCr and 13DyCr have no frequency dependence at zero DC field,and compound 14DyCr have better frequency dependence at low temperature.It shows that the introduction of Cr^? with high spin ground state in this kind of cyano-bridged 3d-4f compounds will lead to the rapid relaxation of QTM effect.