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

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 LnO 8 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.