Complementation and joint contribution of appropriate intramolecular coupling and local ion symmetry to improve magnetic relaxation in a series of dinuclear Dy2 single-molecule magnets

Abstract

A series of lanthanide binuclear complexes with formula [Dy₂(DMOP)₂(NTFA)₄] (1), [Dy₂(DMOP)₂(NTFA)₄(CH₃OH)₂·2H₂O] (1a), [Dy₂(DMOP)₂(BTFA)₄] (2), [Dy₂(DMOP)₂(TTA)₄] (3), [Y₂(DMOP)₂(TTA)₄] (3Y), [Tb₂(DMOP)₂(NTFA)₄] (4), [Tb₂(DMOP)₂(NTFA)₄(CH₃OH)₂·2H₂O] (4a), [Er₂(DMOP)₂(NTFA)₄] (5), [Gd₂(DMOP)₂(NTFA)₄(CH₃OH)₂·2H₂O] (6), and [Gd₂(DMOP)₂(TTA)₄] (7) (DMOP = 2,6-dimethoxyphen, NTFA = 2-naphtoyltrifluoroacetone, BTFA = benzoyltrifluoroacetone, TTA = thenoyltrifluoroacetone) have been structurally and magnetically characterized. They possess nearly the same dinuclear Ln2 cores bridged by double μ₂-phenoxyl oxygen atoms and differ in the peripheral coordinated β-diketonate ligands or coordinated neutral MeOH molecule. The Dy(III)-based derivatives show significant zero-field single-molecule magnet behavior. It is noteworthy that the single-molecule magnet (SMM) performance of 1 was dramatically improved after transforming to 1a with a nearly double energy barrier, which is mostly due to the enhancement of local symmetry around Dy(III) ions in 1a by the introduction of a CH₃OH molecule. In addition, the nature of intramolecular Dy–Dy interaction changed from antiferromagnetic to ferromagnetic coupling. The detailed ab initio calculation reveals the alternate domination of the intramolecular exchange coupling and dipole–dipole interactions in 1 and 1a, respectively. Furthermore, improved SMM performance with a hysteresis temperature of 3 K was observed in diluted samples of 3. In the present work, the joint contribution of intramolecular coupling and local symmetry to improve their dynamic magnetic relaxation was unambiguously affirmed.