Enhancing Energy Barrier of Dysprosium(III) Single-Molecule Magnets by Tuning Magnetic Interactions through Different N-oxide Bridging Ligands

Utilizing different N-oxide ligands to tune Ln-Ln magnetic interactions and their magnetic relaxation behavior, three one-dimensional chain complexes of [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 of [Ln(hfac)3(PzNO)]2 (Ln = Dy(4), Tb(5) and Ho(6), PzNO = pyrazine-N-oxide) were synthesized and characterized respectively. The central LnIII ions of six complexes are all in analogous LnO8 coordination environment. Magnetic investigations indicated that chain complex 1 with neglectable Dy-Dy magnetic interactions through 4,4'BipyNO ligand and low DyIII symmetry (D2d) shows poor slow relaxation behavior with average energy barrier of 11.79 K in 600 Oe dc field. While for complex 4, the relatively stronger Dy-Dy antiferromagnetic interactions (J = -2.36 cm-1) through µ-O PzNO ligand combining with improved DyIII symmetry (near D4d) enhance the Ueff greatly to 226.73 K, which records the highest Ueff for any beta-diketone constructed SMMs and also the third-highest one among all DyIII-only dimers under zero dc field to date. This work also provided another example of conspicuously improving Ln-SMMs energy barrier by the synergic effect of strengthening Dy-Dy magnetic interactions and the improved DyIII symmetry.