| Single-molecule magnets?SMMs?are nano-sized magnets composed of a single molecule that is independent of each other and has no interaction between molecules.They have rich magnetic behaviors of slow magnetic relaxation,spin crossover,quantum tunneling effect and so on.Usually,the SMMs that are only composed of one metal ion in their molecular structures are also called as single-ion magnets?SIMs?.Their interesting quantum physical phenomena and macroscorpic magnet-like behavor have attracted considerable attention.Currently,the design and synthesis of SMMs with high barrier and block temperature is the main research topic in this field.The common method is to select a paramagnetic metal ion possessing large magnetic anisotropy and a suitable ligand to construct targeted complexes.The Dy???ion possessing large magnetic anisotropy,is an ideal spin carrier for constructing SMMs or SIMs.In addition,chiral single molecule magnets not only have the properties of single molecule magnets,may also have the special properties associated with chiral molecular structures such as magneto-chiral dichroism effect?MChD?,chiral optical activity,second harmonic generation?SHG?and ferroelectricity,etc.However,the number of multifunctional chiral molecular magnets reported in literature is rare.In this thesis,using Dy????-diketones intermediates with different polarities to react with chiral enantiomers containing N atoms,we have synthesized a series of chiral multifunctional complexes with SMM/SIM behavors and ferroelectricity properties.Their molecular structures and properties are further studied,in order to explore the main factors that affect the effective barrier of single molecule magnets and single ion magnets.In Chapter 1,we introduce the characteristics and research progress of single molecule magnets,the synthesis and application prospect of chiral complexes and the purpose and significance of this thesis.In Chapter 2,using Dy????-diketones intermediates with different polarities to react with bidentate chiral enantiomers containing N atoms,respectively,we have synthesized four pairs of mononuclear dysprosium enantiomers?1-8?.The molecular structures,SIM behavors,chiral optical activities togather with ferroelectricity were investigated.The results are as follows:?1?Based on ?-diketone Hfac with strong polarity,two pairs of mononuclear Dy???enantiomers with the formulae of Dy?hfac?3·L2NR?1?and Dy?hfac?3·L2NS?2?,[HL2NR]+-[Dy?hfac?4]–?3?and [HL2NS]+[Dy?hfac?4]–?4?were constructed.The structures and properties of two pairs of mononuclear Dy???enantiomers were dramatically controlled by crystallization temperature?The reactants were crystallized at room temperature for 1 and 2,while 3 and 4 crystallized in a refrigerator at 3 °C.?.The enantiomer with coordinated chiral N-donor ligands exhibit enhanced single ion magnet,ferroelectric and chiroptical properties with respect to the other one with protonated chiral N-donor ligands.The results show that the coordination control of chiral ligands can change the symmetry and polarity of molecular structures?The enantiomers of 1 and 2 have low symmetry.Howevre,enantiomers 3 and 4 have high symmetry?,so as to achieve the goal of regulating the properties of molecular materials.?2?Based on ?-diketones Hbta and Hdbm with different polarities,two pairs of mononuclear Dy???enantiomers formulated as Dy?bta?3·L2NR?5?and Dy?bta?3·L2NS?6?,Dy?dbm?3·L2NR?7?and Dy?dbm?3·L2NS?8?were constructed.The magnetic test results show that enantiomers 5-8 have obvious slow relaxation processes under the zero field,and the effective energy barrier for isomers 1,5 and 7 are 16.35,91.6 and 125.1 K,respectively.These results demonstrated that when the strong electron withdrawing groups?-CF3?in the ?-diketone are replaced by benzene rings,the effective energy barriers of the isomers are improved significantly.It is shown that the effective energy barrier of Dy???single ion magnets can be obviously improved by decreasing the polarity of the ligands.In Chapter 3,using Dy????-diketones intermediates Dy?tta?3·2H2O to react with bis-bidentate chiral enantiomers containing N atoms,respectively,we have synthesized a pair of binuclear Dy???enantiomers?9 and 10?.Moreover,their molecular structures,SMM behavors and chiral optical activities were characterized,and the test results were further analyzed and discussed.The effective barrier of isomer 9 is up to 155.9 K,which implies that the effective barrier of Dy???single molecule magnets can be significantly improved by increasing the nuclearities of Dy???ions,compared with the effective energy barrier of aforementioned Dy???single ion magnets. |
PDF Full Text Request