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

Abstract

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 [Dy₂(L)(NO₃)₃(CH₃O)] (1) and [Dy₂(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 Dy^III⋯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 Dy₂ 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.