Syntheses,Crystal Structures And Magnetic Properties Of New 3d-4f Or 4f Polynuclear Metal Complexes

In recent decades, much interest has been focused on the polynuclear metal complexes of 3d-4f or 4f because of their unique magnetic properties like single-molecule magnets(SMMs) and magnetocaloric effect(MCE). With this in mind, we chose polydentate hydroxy-rich ligands reacting with 3d and 4f metal ions or pure LnⅢions by self-assembly approach and obtained twenty new complexes.They have been characterized by X-ray single crystal structure analysis, IR, element analysis, and powder X-ray diffraction(XRD). The magnetic behaviors of them have been analyzed. Among them:1. A family of phenoxo-bridged heterometallic Schiff base trinuclear complexes[Fe2Ln](Ln=Sm/Gd/Tb/Dy) was obtained according to the ligand2-hydroxy-3-methoxy-phenylsalicylaldimine(H2L1). In each complex, two anionic[Fe L2]- units coordinate to the central lanthanide ion as a tetradentate ligand using its four phenoxo oxygens, forming a two-blade propeller-like molecular shape. Magnetic properties show that weak ferromagnetic exchanges between the Fe III and Ln III ions, established by the Gd derivative. The Tb and Dy complexes show no evidence of slow relaxation behavior above 2.0 K. In addition, three new tetranuclear lanthanide clusters [Ln4](Ln= Tb/Dy/Ho) have been obtained by the use of this ligand. These clusters have a planar ″butterfly″ Ln4 core. Among them, [Dy4]and [Ho4] display field-induced slow relaxation of magnetization.2. Three tetranuclear clusters [Zn2Ln2](Ln=Dy/Tb/Ho) have been obtained by using hydroxyl-rich Schiff-base ligand 1,2-Bis(2-hydroxy-3-methoxybenzylidene)hydrazine(H2L2). The structure of three compounds shows that an irregular parallelogram core involving two Ln3+ and two Zn2+ ions are linked by phenol oxygen atoms from four L2- ligands. Ac magnetic measurements suggest that the[Zn2Dy2] cluster behaves as SMM.3. Four novel undecanuclear [Cu9Ln2](Ln = Eu, Gd, Tb, and Dy) isolated clusters have synthesized by using a monoethanolamine(Hmea) ligand. The metallic core,consisting of a beautiful [3×3] [Cu9] grid and two [Ln Cu4] tetragonal pyramids by sharing two [Cu4] planes. The magnetic investigations show a MCE for the [Cu9Gd2]complex and slow relaxation behavior for the [Cu9Tb2] and [Cu9Dy2] species.4. Four pure lanthanide octanuclear clusters [Ln8](Ln= Gd/Tb/Dy/Ho) have been obtained by using a new versatile Schiff base ligand,(E)-Methyl N’-(2-hydroxy-3-methoxybenzylidene)hydrazinecarboxylate(HL3) as the ligand.Each molecular structure can be described as two boat conformation-like tetranuclear units. Magnetism studies reveal that antiferromagnetic Gd…Gd interactions exist in Gd8, which exhibits a significant magnetocaloric effect. In addition, Dy8 exhibits frequency-dependent slow relaxation of the magnetization at zero applied direct current(dc) magnetic field.5. Three unique dodecanuclear lanthanide clusters [Ln12](Ln= Gd/Tb/Dy) with a distorted 4-layered triangular shelf-like molecular structure were reported for the first time. The metal ions are assembled into 4-layered triangular shelf-shaped structures.Magnetic characterization reveals that complex [Gd12] displays a significant cryogenic magnetocaloric effect, while complex [Dy12] exhibits slow relaxation of magnetization.