Large magnetocaloric effect and remarkable single-molecule-magnet behavior in triangle-assembled Ln III6 clusters

Abstract

Two new and interesting polynuclear lanthanide clusters, namely, [Ln₆(acac)₄(HL)₂(THAM)₄(CH₃COCH₃)₂]·2CH₃OH (Ln^III = Gd (1) and Dy (2), Hacac = acetylacetone, H₃L = N′-(2-hydroxy-3-methoxybenzylidene)-6-(hydroxymethyl)picolinohydrazide and THAM = tris(hydroxymethyl)methylaminomethane), were assembled by using a polydentate ligand (H₃L) reacting with β-diketonate salts (Ln(acac)₃·2H₂O, Ln^III = Gd and Dy) and the auxiliary ligand THAM, respectively. Single-crystal X-ray structures reveal that 1 and 2 are hexanuclear clusters which are linked by perfect Ln₃ triangles via μ₃-O and μ₂-O atoms. The magnetic investigations reveal that 1 displays cryogenic magnetic refrigeration properties with large magnetic entropy (−ΔS_m = 35.4 J kg⁻¹ K⁻¹ with ΔH = 7.0 T and T = 2.0 K). Remarkably, alternating current (ac) magnetic susceptibility measurement reveals that 2 exhibits typical SMM behavior with U_eff/k_B = 50.8 K and pre-exponential factor τ₀ = 1.5 × 10⁻⁶ s. It is one of the rare polynuclear Dy₆ SMMs under zero dc field.