Design, Syntheses And Magnetic Properties Of Polynuyclear Ln-based Complexes

Single-mo lecular magnets?SMMs?have attracted increasing interest in the field of nanomagnetic materials due to magnetic bistability and slow magnetic relaxation behavior.In this thesis,a series of novel polynuc lear Ln-based complexes with fascinating structures were prepared by using O-vanillin or Schiff-base and high anisotropic Dy^? ion,and their structures and magnetic properties were systematically investigated.More details are as follows:1.We presented a supramolecular Dy₆?1?cluster via coupling highly anisotropic Dy₃ triangular fragments with multi-fo ld mode which displayed obvious SMM behavior under zero applied direct current?dc?field.While complex Dy₆Na₂?2?,possessing identical coordination geometries to Dy₆ shows only slow relaxation.The dramatic changes in the distinct dynamic magnetic behaviors could be attributed to the distortion of the coordination geometry.Futhermore,the anisotropy axes of complex 1 were arranged similar to a parallelogram.2.The application of a new flexib le long acylhydrazone ligand H₂L¹ results in the self-assembly of Dy₄L₄¹?3;quadruple-stranded helicate?,Dy₈L₈¹?4;dual triple-strand helicate?and Dy₁₂L₁₂¹?5;octahedral cage?.The complexes 3-4 show slow magnetic relaxation,but complex 5 exhibits obvious SMM behavior in zero dc field.To date,few lanthanide single-molecule magnets have been reported that have more than ten nuclearities.3.In this chapter,we designed a long chain asymmetrical Schiff-base ligand.Three novel[2×2]Dy₂Fe₂L₄²?6-8?grid-like complexes were self-assembled using this long chain asymmetrical Schiff-base ligand,high anisotropic Dy^? ion and Fe^? ion,but different terminal ligands.These complexes display different relaxation behavior.In particular,complex 6 exhibits slow magnetic relaxation behavior in zero dc field.However,no spin crossover behaviors were observed in these three complexes.