Magnetic anisotropy of transition metal and lanthanide ions in pentagonal bipyramidal geometry

The magnetic anisotropy associated with a pentagonal bipyramidal (PBP) coordination sphere is examined on the basis of experimental and theoretical investigations. The origin and the characteristics of this anisotropy are discussed in relation to the electronic configuration of the metal ions. The effects of crystal field, structural distortion, and a second-coordination sphere on the observed anisotropies for transition meal and lanthanide ions are outlined. For the Ln derivatives, we focus on compounds showing SMM-like behavior (i.e. slow relaxation of their magnetization) in order to highlight the essential chemical and structural parameters for achieving strong axial anisotropy. The use of PBP complexes to impart controlled magnetic anisotropy in polynuclear species such as SMMs or SCMs is also addressed. This review of the magnetic anisotropies associated with a pentagonal bipyramidal coordination sphere for transition metal and lanthanide ions is intended to highlight some general trends that can guide chemists towards designing a compound with specific properties.

Enhancing the energy barrier and hysteresis temperature in two benchtop-stable Ho(iii) single-ion magnets

The energy barrier and hysteresis temperature in two benchtop-stable D_5h-symmetry Ho^III single-ion magnets were significantly enhanced via the variation of the halogen anion. The coexistence of a high energy barrier of 418 K and hysteresis temperature of 15 K was observed in the bromide-ion containing Ho^III single-ion magnet.

Enhancing the energy barrier by replacing the counterions in two holmium(iii)-pentagonal bipyramidal single-ion magnets

Based on a phosphine oxide ligand, HMPA (hexamethylphosphoric triamide), two mononuclear Ho^III-pentagonal bipyramidal complexes were synthesized with the formulas [Ho(HMPA)₂(H₂O)₅]₂Cl₆·2HMPA·2H₂O (1) and [Ho(HMPA)₂(H₂O)₅]Br₃·2HMPA (2). Single-crystal X-ray diffraction results show that all Ho^III ions in both the two complexes are hepta-coordinated and are located in pentagonal bipyramidal {HoO7} coordination polyhedrons constructed by two axial HMPA ligands and five equatorial water molecules. However, due to the employment of different halide ions as counterions, the second coordination sphere surrounding each [Ho(HMPA)₂(H₂O)₅]³⁺ moiety is different in the two complexes: in 1, three Cl^- ions, one water molecule and one HMPA ligand; in 2, three Br^- ions and two HMPA ligands. Ac magnetic susceptibilities under zero dc field show that both the two complexes are single-ion magnets with effective energy barriers of 290 K and 320 K for 1 and 2, respectively. Compared with 1, the enhancement in the energy barrier of 2 is believed to be induced mainly by the change in the second coordination sphere rather than the minor differences in the {HoO7} polyhedrons.

Pentagonal Bipyramidal Ln(III) Complexes Containing an Axial Phosphine Oxide Ligand: Field-induced Single-ion Magnetism Behavior of the Dy(III) Analogues

A series of neutral homologous complexes [(L)Ln(Cy₃PO)Cl] {where Ln = Gd (1), Tb (2), Dy (3), and Er (5)} and [(L)Dy(Ph₃PO)Cl] (4) [H₂L = 2,6-diacetylpyridine bis-benzoylhydrazone] were isolated. In these complexes, the central lanthanide ion possesses a pentagonal bipyramidal geometry with an overall pseudo D_5h symmetry. The coordination environment around the lanthanide ion comprises of three nitrogen and two oxygen donors in an equatorial plane. The axial positions are taken up by a phosphine oxide (O donor) and a chloride ion. Among these compounds, the Dy(III) (3 and 4) analogues were found to be field-induced single-ion magnets.

Substituent effects of auxiliary ligands in mononuclear dibenzoylmethane DyIII/ErIII complexes: single-molecule magnetic behavior and luminescence properties

The single-molecule magnetic behavior and luminescence of [(dbm)₃Ln(dmbipy)] and [(dbm)₂Ln(dmobipy)(NO₃)] are significantly modified by replacing the substituents of auxiliary ligands.

A square antiprism dysprosium single-ion magnet with an energy barrier over 900 K

A stable and high-performance molecule displays a reversal barrier >900 K, which is the highest among square antiprismatic dysprosium single-ion magnets.

Two mononuclear dysprosium(iii) complexes with their slow magnetic relaxation behaviors tuned by coordination geometry

We report here two field-induced single-ion magnets of Dy(iii), which present octahedral and pentagonal–bipyramidal coordination geometries, respectively, with their magnetic performances tuned by the coordination geometries of Dy(iii).