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

A family of dinuclear dysprosium cores bridged by different ligands within a polyoxometalates (POMs) framework, (TBA)(8.5)H1.5[(PW11O39)(2)Dy2X2(H2O)(2)]center dot 6H(2)O (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 mu-eta(1:)eta(2)-acetato ligands. Notably, the low-temperature fluorescence spectra of 13 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.