Butterfly-shaped tetranuclear Ln4 clusters showing magnetic refrigeration and single molecule-magnet behavior

Abstract

Three new Ln₄ clusters based on a bidentate Schiff base ligand having formulae [Ln₄(μ₃-OH)₂L₆(acac)₄]·xCH₃CN (Ln(III) = Eu(1), Gd(2) and Dy(3), x = 1 for 1, x = 2 for 2, and x = 0 for 3, HL = 5-(4-o-hydroxybenzylidene)-8-hydroxylquinoline and acac = acetylacetone) have been successfully synthesized and completely characterized. The structures of 1–3 are similar to each other except for the nature of the central ion and the number of free acetonitrile molecules. The four Ln^III ions are coplanar and clusters 1–3 have a butterfly-shaped arrangement. Magnetic studies show that cluster 2 displays a weak antiferromagnetic exchange interaction between nearby Gd^III centers and exhibits magnetic refrigeration with maximum −ΔS_m = 18.85 J kg⁻¹ K⁻¹ (ΔH = 7.0 T at 2.5 K). Alternating current (ac) magnetic susceptibility measurement of 3 indicates that 3 demonstrates SMMs behavior under a zero direct-current (dc) field, with an effective energy barrier (ΔE/k_B) of 79.15 K and a pre-exponential factor τ₀ = 5.82 × 10⁻⁸ s.