Solvent-Mediated Structural Control of Single-Molecule Magnet Performance in Tetranuclear Dysprosium Clusters.

A diacylhydrazone ligand (H4L) was synthesized from 3-hydroxy-2-naphthoylhydrazine and glyoxal. Its reactions with dysprosium(III) salts, mainly by tuning the reaction solvents, gave three tetranuclear dysprosium clusters: [Dy4(HL)4(CH3OH)4]·8CH3OH (1), [Dy4(HL)4(CH3OH)2(DMF)2]·2CH3OH·2DMF (2), and [Dy4(HL)4(DMF)4]·3DMF (3). The three clusters have similar pseudosquare ring-like skeletons with two Dy(III) ions on each edge, double-connected through an acyl oxygen atom and a phenolic oxygen atom. The difference lies in the coordinated solvent molecules, which are four CH3OH molecules for 1, two CH3OH and two DMF molecules for 2, and four DMF molecules for 3. The ac magnetic tests under fields showed slow magnetic relaxation for 1; however, the other two complexes are single-molecule magnets (SMM). Obviously, the progressive replacement of the coordinated solvent molecules of methanol by DMF systematically slows down the magnetic relaxation and improves the SMM performance. This is a typical example of using two types of coordination solvent molecules to tune SMM performance, providing some hints for enhancing cluster-based SMM performance. Theoretical calculations further elucidated the solvent-mediated SMM tuning effect by exploring the magneto-structural correlation.