Effect of Bridging Ligands on Magnetic Behavior in Dinuclear Dysprosium Cores Supported by Polyoxometalates

Abstract

A family of dinuclear dysprosium cores bridged by different ligands within a polyoxometalates (POMs) framework, (TBA)_8.5H_1.5[(PW₁₁O₃₉)₂Dy₂X₂(H₂O)₂]·6H₂O (X = OH (1), F (2), OAc (3); TBA = tetra- n-butylammonium), was successfully synthesized and structurally characterized. Magnetic studies indicate that the bridging ligands can significantly affect the magnetic behaviors, with 1 and 3 showing antiferromagnetic coupling and 2 bridged by fluoride ions showing ferromagnetic interaction. 1 and 2 behaved as single-molecule magnets (SMMs) with the thermally activated energy barrier of 98(5) and 74(6) cm^-1 under zero dc filed, respectively, whereas no SMM behavior was observed for 3 bridged by two μ-η¹:η²-acetato ligands. Notably, the low-temperature fluorescence spectra of 1-3 provide valuable information on the energy levels, which are consistent with the anisotropic barriers determined by magnetic measurements. These results offer an insight into the magneto-optical correlation. Furthermore, the effective energy barrier of 1 reaches a breakthrough among all POM-based SMMs.