Macrocycle based dinuclear dysprosium( iii ) single molecule magnets with local D 5h coordination geometry

Abstract

Bis(pyrazolato)-bridged macrocycles are shown to serve as scaffolds for Dy 2 single molecule magnets with control over the relative orientation of anisotropy axes.

Targeted approaches for manipulating the coordination geometry of lanthanide ions are a promising way to synthesize high-performance single-molecule magnets (SMMs), but most of the successful examples reported to date focus on mononuclear complexes. Herein, we describe a strategy to assemble dinuclear SMMs with Dy III ions in approximate D 5h coordination geometry based on pyrazolate-based macrocyclic ligands with two binding sites. A Dy4 complex with a rhomb-like arrangement of four Dy III as well as two dinuclear complexes having axial chlorido ligands (Dy2·Cl and Dy2 ·Cl) were obtained; in the latter case, substituting Cl − by SCN − gave Dy2·SCN. Magneto-structural studies revealed that the μ-OH bridges with short Dy–O bonds dominate the magnetic anisotropy of the Dy III ions in centrosymmetric Dy4 to give a vortex type diamagnetic ground state. Dynamic magnetic studies of Dy4 identified two relaxation processes under zero field, one of which is suppressed after applying a dc field. For complexes Dy2·Cl and Dy2 ·Cl, the Dy III ions feature almost perfect D 5h environment, but both complexes only behave as field-induced SMMs ( U eff = 19 and 25 K) due to the weak axial Cl − donors. In Dy2·SCN additional MeOH coordination leads to a distorted D 2d geometry of the Dy III ions, yet SMMs properties at zero field are observed due to the relatively strong axial ligand field provided by SCN − ( U eff = 43 K). Further elaboration of preorganizing macrocyclic ligands appears to be a promising strategy for imposing a desired coordination geometry with parallel orientation of the anisotropy axes of proximate Dy III ions in a targeted approach.

Bis(pyrazolato)-bridged macrocycles are shown to serve as scaffolds for Dy 2 single molecule magnets with control over the relative orientation of anisotropy axes.

Targeted approaches for manipulating the coordination geometry of lanthanide ions are a promising way to synthesize high-performance single-molecule magnets (SMMs), but most of the successful examples reported to date focus on mononuclear complexes. Herein, we describe a strategy to assemble dinuclear SMMs with Dy III ions in approximate D 5h coordination geometry based on pyrazolate-based macrocyclic ligands with two binding sites. A Dy4 complex with a rhomb-like arrangement of four Dy III as well as two dinuclear complexes having axial chlorido ligands (Dy2·Cl and Dy2 ·Cl) were obtained; in the latter case, substituting Cl − by SCN − gave Dy2·SCN. Magneto-structural studies revealed that the μ-OH bridges with short Dy–O bonds dominate the magnetic anisotropy of the Dy III ions in centrosymmetric Dy4 to give a vortex type diamagnetic ground state. Dynamic magnetic studies of Dy4 identified two relaxation processes under zero field, one of which is suppressed after applying a dc field. For complexes Dy2·Cl and Dy2 ·Cl, the Dy III ions feature almost perfect D 5h environment, but both complexes only behave as field-induced SMMs ( U eff = 19 and 25 K) due to the weak axial Cl − donors. In Dy2·SCN additional MeOH coordination leads to a distorted D 2d geometry of the Dy III ions, yet SMMs properties at zero field are observed due to the relatively strong axial ligand field provided by SCN − ( U eff = 43 K). Further elaboration of preorganizing macrocyclic ligands appears to be a promising strategy for imposing a desired coordination geometry with parallel orientation of the anisotropy axes of proximate Dy III ions in a targeted approach.