Rare CH3O-/CH3CH2O--bridged nine-coordinated binuclear Dy-III single-molecule magnets (SMMs) significantly regulate and enhance the effective energy barriers

摘要

Based on a multidentate Schiff-base ligand, N,N'-bis(2-hydroxy-5-methyl-3-formylbenzyl)-N,N'-bis-(pyridin-2-ylmethyl)ethylenediamine (H2L), two binuclear Dy-III compounds, with formulas [Dy-2(L)(NO3)(3)(CH3O)] (1) and [Dy-2(L)(NO3)(3)(CH3CH2O)] (2), have been synthesized under different solvent systems. The Dy-III ions in 1 and 2 adopt monocapped square antiprism coordination geometries, while different structural distortions can be observed. The two Dy-III ions in 1 and 2 are bridged by two phenoxide atoms of one L2- ligand and one bridged CH3O-/CH3CH2O- oxygen node, leading to an approximate fusiform Dy2O3 core. The different Dy-III-O-bridged node distances, Dy-III-O-bridged node-Dy-III angles and (DyDyIII)-Dy-III distances can be observed. Magnetic studies reveal that 1 and 2 display slow magnetic relaxation behaviours under a zero direct-current field with the effective energy barriers (U-eff) of 114.17 K and 171.23 K, respectively. Furthermore, compound 2 possesses the highest U-eff in nine-coordinated Dy-2 compounds. The M versus H data exhibit weak butterfly-shaped hysteresis loops at 2 K for 2. The rare CH3O-/CH3CH2O--bridged nine-coordinated binuclear Dy-III single-molecule magnets (SMMs) significantly regulate and enhance the U-eff of compounds 1 and 2. To deeply understand their different magnetic behaviours, the magnetic anisotropies and magnetic interactions of 1 and 2 were studied by ab initio calculations. These findings demonstrate an efficient approach for regulating and enhancing the magnetic anisotropy barriers using a bridged CH3O- anion or CH3CH2O- anion.