Synthesis And Magnetic Properties Of Lanthanide Complexes Based On Schiff-Base/Carboxylic Acid Ligands

Exploiting a desirable strategy to design and synthesize high-performance single-molecule magnets(SMMs)continues to be of great interest.In this thesis,the lanthanide metal ions with large uniaxial anisotropy are selected as the paramagnetic centers.By changing of the external environment,the influence on structure and magnetic behavior are being explored.Here,several lanthanide complexes have been successfully synthesized based on two types of ligands and magnetically characterized in detail.The relationship between the structures and the magnetisms of the complexes were preliminarily discussed.1.Nine lanthanide magnetic complexes were successfully synthesized by the slightly modification of the reaction conditions with Schiff base organic ligands and metal DyⅢ and ErⅢ ions as paramagnetic centers.Single-crystal structure analysis determines that all the complexes 1-9 present dinuclear cores.The metal centers of 1-8 are mainly linked by phenolic groups,the complex 9 is connected by the moieties of the organic ligand.Among them,the transverse coordination atoms of the complexes 1,3,4 and 6 exhibit a local hula,hoop-like geometry,whereas the additional μ2-OH2 bridge in 2,4 an d 7 induces a large bend in the geometrical configuration.For 8,the carboxylic groups exhibit both chelate and bridged coordination mode.Magnetic studies show that the complexes 1,4,8 and 9 exhibit slow relaxation of the magnetization.Through the analysis of relationship between the structures and the magnetisms,it can be concluded that maintaining the configuration of a local hula-hoop-like geometry is important for controlling the magnetic behavior of SMMs.Meanwhile,the strategic change of the extent of conjugation in the backbone of ligands may affects the redistribution of the charge around the metal centers,which affects the SMM/non-SMM behavior.The researches provides theoretical foundation for the design of magnetic complexes.2.Using 4,4’,4"-tricarboxytriphenylamine(H3TCA)as ligand and DyⅢ,YⅢ,ErⅢ,YbⅢions as metal centers,four lanthanide metal organic frameworks were successfully synthesized.Structural analysis reveals that complexes 10-13 features a three-dimensional(3D)framework based on well-isolated one-dimensional metal/oxygen ribbons.Complexes 10 and 11 represent the unusual pentanuclear units constructed by cubane-like[Ln4O4](｛Ln4｝)clusters and the additional Ln center,while the asymmetric unit of complexes 12 and 13 contains two metal ions combined with other two centrosymmetrically-related metal ions to form a{Ln4} core which contains two Ln3 triangular units sharing the edge.The H3TCA ligand presents rich coordination modes on the construction of complexes 10-13.The four metal organic frameworks show peculiar topologies which possess magnetic and optical properties.Complexes 10 and 12 exhibit slow magnetic relaxation behavior;complexes 12 and 13 provide near-infrared solid fluorescence.Thus,the complex 12 would be anticipated as multifunctional materials.