Enhancing the Magnetic Behaviors of Dy2 Complexes by Modulating the Crystal Field Environment with Different μ-O Bridging Ligands

Four similar dinuclear lanthanide complexes have been synthesized by linking two [Ln(hfac)2–3] units (hfac stands for hexafluoroacetylacetone) with different μ-O bridging ligands. The 2,2′-bipyridine-N-oxide ligand (bmpo) constructed two centrosymmetric complexes [Ln2(hfac)6(bmpo)2] (Ln = Dy(1), Tb(2)), with nine-coordinated LnIII ions showing Cs low symmetry, while the ligand di(2-pyridyl)methanediol (py2C(OH)2) formed another two compounds [Ln2(hfac)4(py2C(OH)O)2] (Ln = Dy(3), Tb(4)), with two kinds of eight-coordinated LnIII ions exhibiting improved symmetries of D4d and D2d. Magnetic analysis reveals that Dy2 complex 1 shows intramolecular antiferromagnetic coupling (J = −1.07 cm−1) and no relaxation process above 2.0 K even in a 1000 Oe dc field, owing to the low symmetry of DyIII ions, while the similar Dy2 complex 3 with improved DyIII symmetry shows ferromagnetic coupling (J = 1.17 cm−1), which induces a 1000 Oe dc field-induced two-step magnetization relaxation processes with effective energy barrier Ueff = 47.4 K and 25.2 K for the slow relaxation and fast relaxation processes, respectively. This study proves again that the improved symmetry combined with intramolecular ferromagnetic interactions, both mediated by bridging ligands, can enhance the DyIII anisotropy, further quench the quantum tunneling of the magnetization, and finally, enhance the magnetic behavior of LnIII-based systems.