Solvent-tuned magnetic exchange interactions in Dy₂ systems ligated by a μ-phenolato heptadentate Schiff base

A series of binuclear dysprosium compounds, namely, [Dy(api)]₂ (1), [Dy(api)]₂·2CH₂Cl₂ (2), [Dy(Clapi)]₂·2C₄H₈O (3), and [Dy(Clapi)]₂·2C₃H₆O (4) (H₃api = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazoline; H₃Clapi = 2-(2'-hydroxy-5'-chlorophenyl)-1,3-bis[3'-aza-4'-(2''-hydroxy-5''-chlorophenyl)prop-4'-en-1'-yl]-1,3-imidazolidine), have been isolated by the reactions of salen-type ligands H₃api/H₃Clapi with DyCl₃·6H₂O in different solvent systems. Structural analysis reveals that each salen-type ligand provides a heptadentate coordination pocket (N₄O₃) to encapsulate a Dy^III ion and all of the Dy^III centers in 1-4 adopt a distorted square antiprism geometry with D _4d symmetry. Magnetic studies showed that compound 1 did not exhibit single-molecule magnetic (SMMs) behavior. With the introduction of different lattice solvents, compounds 2-4 showed filed-induced slow magnetic relaxation with barriers U _eff of 18.2 K (2), 28.0 K (3) and 16.4 K (4), respectively. Ab initio calculations were employed to interpret the magnetization behavior of 1-4. The combination of experimental and theoretical data reveal the importance of the weak exchange interaction between the Dy^III ions in the observation of slow magnetic relaxation, and a relaxation mechanism has been developed to rationalize the observed difference in the U _eff values. The different lattice solvents influence Dy-O-Dy bond angles and thus alter the torsion of the square antiprism geometry, consequently resulting in distinct magnetic interactions and the magnetic behavior.