Solvent-tuned magnetic exchange interactions in Dy(2) systems ligated by a μ-phenolato heptadentate Schiff base

A series of binuclear dysprosium compounds, namely, [Dy(api)](2) (1), [Dy(api)](2)·2CH(2)Cl(2) (2), [Dy(Clapi)](2)·2C(4)H(8)O (3), and [Dy(Clapi)](2)·2C(3)H(6)O (4) (H(3)api = 2-(2-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazoline; H(3)Clapi = 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 H(3)api/H(3)Clapi with DyCl(3)·6H(2)O in different solvent systems. Structural analysis reveals that each salen-type ligand provides a heptadentate coordination pocket (N(4)O(3)) 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.