A new dinuclear dysprosium (III) single-molecule magnet (SMM), Dy₂ (hynad) ₂ (dbm) ₄·DMF (1·DMF), supported by the bulky anionic N–O bridging ligand, N-hydroxy-1, 8-naphthalimide (hynadˉ), has been synthesized. The deprotonated hynadˉ ligands enforce a robust and nearly planar Dy₂ (µ-OR) ₂^4+ core, which is surrounded by the sterically demanding dibenzoylmethanoate (dbmˉ) coligands. Each DyIII center adopts a distorted triangular dodecahedral geometry, generating a highly axial crystal field. AC magnetic measurements reveal zero-field SMM behavior, with slow relaxation of the magnetization persisting up to 16 K, as well as open magnetic hysteresis loops observed by µSQUID magnetometry up to 3. 5 K. Analysis of the AC susceptibility data yields an effective energy barrier for magnetization reversal of U₄₅₅ = 171 K. µSQUID studies disclose a characteristic double-S-shaped hysteresis, consistent with an antiferromagnetically coupled ground state separated by a small energy gap from a low-lying ferromagnetic excited state. Ab initio calculations confirm the strongly axial mJ = ±15/2 ground Kramers doublets for both Dy^III ions, with the magnetic anisotropy axes oriented nearly perpendicular to the Dy₂ (µ-OR) ₂^4+ plane. The combined experimental and theoretical analysis demonstrates that the Dy···Dy interaction is weak and predominantly dipolar in nature, with thermal population of the excited exchange-coupled state enabling the observed slow magnetic relaxation.
Armenis et al. (Thu,) studied this question.