Replacement of Carboxylate Ligand Substituent on Modulation of Structures and Magnetic Properties in Salen-Type Dinuclear Dy(III) Complexes

Three salen-type centrosymmetric dinuclear Dy(III) complexes, [Dy-2(Hhms)(2)(C(CH3)(3)COO)(2)(H2O)(4)](NO3)(2) (1), [Dy-2(Hhms)(2)(C14H9COO)(2)(C2H5OH)(2)(CH3OH)(2)] [ZnCl4] (2), and [Dy-2(Hhms)(2)(C6H3(NH2)(2)COO)(2)Cl-2]center dot 2CH(3)CN (3) (H(2)hms=(2-hydroxy-3-methoxybenzylidene)-semicarbazide), were isolated with different substituted carboxylic acid ligand, and were characterized structurally and magnetically. Structural analyses illustrate that the Dy(III) ions in complexes 1 and 2 maintain similar monocapped square-antiprism geometries, but the coordination mode of carboxylate in 1 is different from that in 2; complexes 2 and 3 possess similar phenoxy oxygen and carboxylate bridged structure whereas the coordination geometries around the Dy(III) ions are different between 3 and 2 due to the difference of coordinated small molecules. Magnetic characterizations reveal that significant single-molecule magnet (SMM) behavior was observed under zero dc field for complex 3, with an effective energy barrier to the reversal of magnetization of 96 K. Conversely, complex 1 only showed fast quantum tunneling relaxation even 2 was SMM-silent. Furthermore, the magneto-structural correlations in these Dy-2 complexes were discussed. The results indicate that utility of carboxylate ligand substituent can give rise to good modulation in the molecular anisotropy and symmetry, hence the enhanced magnetic relaxation.