Hydroxide-Free Cubane-Shaped Tetranuclear [Ln₄] Complexes

Abstract

The reaction of the lanthanide(III) chloride salts [Gd(III), Tb(III), and Dy(III)] with a new chelating, flexible, and sterically unencumbered multisite coordinating compartmental Schiff-base ligand (E)-2-((6-(hydroxymethyl)pyridin-2-yl)methyleneamino)phenol (LH2) and pivalic acid (PivH) in the presence of triethylamine (Et3N) affords a series of tetranuclear Ln(III) coordination compounds, [Ln4(L)4(μ2-η(1)η(1)Piv)4]·xH2O·yCH3OH (1, Ln = Gd(III), x = 3, y = 6; 2, Ln = Tb(III), x = 6, y = 2; 3, Ln = Dy(III), x = 4, y = 6). X-ray diffraction studies reveal that the molecular structure contains a distorted cubane-like [Ln4(μ3-OR)4](+8) core, which is formed by the concerted coordination action of four dianionic L(2-) Schiff-base ligands. Each lanthanide ion is eight-coordinated (2N, 6O) to form a distorted-triangular dodecahedral geometry. Alternating current susceptibility measurements of complex 3 reveal frequency- and temperature-dependent two-step out-of-phase signals under zero direct current (dc) field, which is characteristic of single-molecule magnet behavior. Analysis of the dynamic magnetic data under an applied dc field of 1000 Oe to fully or partly suppress the quantum tunneling of magnetization relaxation process affords the anisotropic barriers and pre-exponential factors: Δ/kB = 73(2) K, τ0 = 4.4 × 10(-8) s; Δ/kB = 47.2(9) K, τ0 = 5.0 × 10(-7) s for the slow and fast relaxations, respectively.

New salen-type dysprosium(III) double-decker and triple-decker complexes

“…Upon cooling to 20 K, the v M T values for complexes 1 and 2 decrease slightly to 9.7 and 24.0 cm 3 K/mol and then rapidly drop to 8.4 and 18.7 cm 3 K/mol at 2 K. For complex 1, this decrease is partly due to crystal-field effects in which the thermal depopulation of M J sublevels is involved. In compound 2, the v M T value drops even deeper, which can be attributed to combining both the crystal field effect and the antiferromagnetic coupling between Dy 3+ ions [40]. Variable field reduced magnetization experiments were conducted with an applied magnetic field in the range of 10-60,000 G, in the temperature range from 2 to 4 K. The results are shown in Fig.…”

A salen-type Dy4 single-molecule magnet with an enhanced energy barrier and its analogues

“…Fitting of the Cole-Cole plots using the sums of two modified Debye functions 31 gives rela- Fig. 14d, 23 In order to further confirm the single molecule magnetic properties for complex 1, isothermal magnetization experiments have been performed at 1.8 K. However, a very narrow simple sigmoidal hysteresis, the signature of slight anisotropy, 32 was observed. Fig.…”

Single-Molecule Toroics and Multinuclear Lanthanide Single-Molecule Magnets

“…In 2014, E. Colacio reported the hydroxide-free cubane-shaped Dy 4 complex assembled by using compartmental Schiff base ligand and pivalic acid [46]. As shown in Fig.…”