Enhancing the energy barrier of dysprosium(iii) single-molecule magnets by tuning the magnetic interactions through different N-oxide bridging ligands

Abstract

Using different N-oxide ligands to tune the Ln–Ln magnetic interactions and their magnetic relaxation behaviors, herein, three one-dimensional chain complexes, [Ln(hfac)₃(4,4′BipyNO)]_∞ (Ln = Dy(1), Tb(2) and Ho(3); 4,4′BipyNO = 4,4′-bipyridine-N,N′-dioxide), and three dinuclear complexes, [Ln(hfac)₃(PzNO)]₂ (Ln = Dy(4), Tb(5) and Ho(6); PzNO = pyrazine-N-oxide), were synthesized and characterized. The central Ln^III ions of the six complexes are in an analogous LnO₈ coordination environment. Magnetic investigations indicated that the chain complex 1 with negligible Dy–Dy magnetic interactions through the 4,4′BipyNO ligand and low Dy^III symmetry (D_2d) showed a poor slow relaxation behavior with the average energy barrier of 11.79 K under a 600 Oe dc field. However, for the complex 4, the relatively stronger Dy–Dy antiferromagnetic interactions (J = −2.36 cm⁻¹) through the μ-O PzNO ligand combined with an improved Dy^III symmetry (near D_4d) significantly enhance the U_eff to 226.73 K, which records the highest U_eff for any beta-diketone constructed SMMs and also the third-highest one among all Dy^III-only dimers under zero dc field to date. This study also provides another example of conspicuously improving the energy barrier of Ln-SMMs by the synergistic effect of strengthened Dy–Dy magnetic interactions and improved Dy^III symmetry.