Single-Molecule Magnet Behavior Enhanced by Synergic Effect of Single-Ion Anisotropy and Magnetic Interactions

As the simplest entity carrying intramolecular magnetic interactions, a dinuclear lanthanide complex serves as a model to investigate the effects of magnetic interactions on relaxation of magnetization, and importantly, it proves to be an efficient method to obtain robust single-molecule magnets via improving the communication between lanthanide centers. Here, three Dy<sub>2</sub> complexes (<b>1</b>, <b>2</b>, <b>3</b>) with a similar structural motif, namely, [Dy<sub>2</sub>­(HL)<sub>2</sub>­(NO<sub>3</sub>)<sub>2</sub>­(CH<sub>3</sub>CN)<sub>2</sub>]·2CH<sub>3</sub>­CN (<b>1</b>), [Dy<sub>2</sub>­(HL)<sub>2</sub>­(NO<sub>3</sub>)<sub>2</sub>­(DMF)<sub>2</sub>]·2H<sub>2</sub>O (<b>2</b>), and Dy<sub>2</sub>­(HL)<sub>2</sub>­(NO<sub>3</sub>)<sub>2</sub>­(DMF)<sub>4</sub> (<b>3</b>), were successfully assembled. One critical difference found in this series of complexes is that the Dy center in complex <b>3</b> is coordinated by one more solvent molecule. Surprisingly, complex <b>3</b> exhibits the best magnet-like behavior, as evidenced by the high effective barrier and butterfly-type hysteresis, although the crystal field effect around Dy ions is weakened heavily. <i>Ab initio</i> calculations revealed the crucial reason is the significant synergic effect between single-ion anisotropy and magnetic interactions, i.e., not only the axiality of the Dy ion is improved efficiently but also the exchange magnetic interactions increased to the same order of magnitude to the dipolar interaction in <b>3</b>. This effect mainly benefits from the elaborate modification of the local coordinate environment around the Dy ion, which results in a special arrangement of anisotropy axes different from the other two complexes. It demonstrates that the magnetic interactions could be effectively enhanced by means of deliberate local structural modulation.