Abstract

Three di-nuclear Dy^III complexes [Dy₂(H₂L)₂(tfa)]·Cl·3DMF (1), [Dy₂(H₂L)₂(MeO)(SCN)]·MeOH (2) and [Dy₂(H₂L)₂(MeOH)Cl]·Cl·2MeOH (3) were synthesized and structurally and magnetically characterized. The Dy1/Dy2 centers in these complexes are all nine-coordinate with spherical capped square antiprism (local C₄v symmetry) environments. All complexes display single-molecule magnet (SMM) behavior under zero applied dc field with their properties dependent on the nature of the magnetic interactions between the Dy^III ions. Ab initio calculations substantiate that all Dy^III ions show a weakly axial crystal-field environment with the exception of one of the Dy^III ions in complex 2. The ground Kramers doublets show modest amounts of quantum tunneling of magnetization that gets blocked by the interaction between the Dy^III ions, leading to a thermally activated slow relaxation of magnetization. The interaction between the ions is ferromagnetic and mostly originates from the dipolar interaction. However, anti-ferromagnetic intermolecular interaction plays an important role and in the case of complex 2 it is sufficiently strong to mask the ferromagnetic intramolecular interaction.