Asymmetric Binuclear Dysprosium Single-Molecule Magnets Synthesized from a Peripheral-Protected Nonequivalent Chelation Strategy

As a kind of special binuclear dysprosium single-molecule magnet ({Dy2}-SMM), the asymmetric {Dy2}-SMMs feature two Dy centers that locate in distinct ligand fields. Such an asymmetric structure allows to locally modulate a special part of the magnet while maintaining original features of other parts, thus favoring more delicate and targeted tuning of the single-ion anisotropy of the Dy center and magnetic interactions between Dy centers. Yet, they are still rare due to the difficulty in synthesis. Herein, we report three asymmetric {Dy2}-SMMs, namely, [Dy2(tmsa)(MeOsa)(H2O)2] (NO3)2·CH3OH (1), [Dy2(tmsa)(sa)2(H2O)]NO3 (2), and [Dy2(tmsa)(Fsa)(H2O)2] (NO3)2·5H2O·CH3OH (3), where H3tmsa, HMeOsa, Hsa, and HFsa represent tris[(3-methoxysalicylidene)aminoethyl]amine, 3-methoxysalicylaldehyde, salicylaldehyde, and 3-fluorinesalicylaldehyde, respectively. They were prepared by a peripheral-protected nonequivalent chelating strategy, wherein a single tmsa3– ligand uses two distinct chelating pockets to encapsulate two Dy ions while providing peripheral protection. Significantly, salicylaldehyde-based auxiliary ligands bearing different substituents, including HMeOsa, Hsa, and HFsa, have fine-tuned the local ligand fields of the Dy ions successfully. 1–3 thus show different slow magnetic relaxation behaviors, with the highest efficient energy barriers (Ueff) of 79, 154, and 110 K, respectively. This work provides an efficient strategy for the achievement of new asymmetric {Dy2}-SMMs and the fine-tuning of the relaxation behavior of these special SMMs.