An investigation into the magnetic interactions in a series of Dy2 single-molecule magnets

Three di-nuclear DyIII 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 the properties dependent on the nature of the magnetic interactions between the DyIII ions. Ab initio calculations substantiate that all DyIII ions show a weakly axial crystal-field environment with the exception of one of the DyIII ions in complex 2. The ground Kramers doublets show modest amounts of quantum tunneling of magnetization that becomes blocked by the interaction between the DyIII ions, leading to 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 is sufficiently strong to mask the ferromagnetic intramolecular interaction.