Large magnetocaloric effect and remarkable single-molecule-magnet behavior in triangle-assembled LnIII6 clusters

Two new and interesting polynuclear lanthanide clusters, namely, [Ln6(acac)4(HL)2(THAM)4(CH₃COCH₃)2]·2CH3OH (LnIII = 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 ligands (H3L) reacting with the β-diketonate salts (Ln(acac)3·2H2O, LnIII = Gd and Dy) and the auxiliary ligand THAM, respectively. Single-crystal X-ray structure reveals 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 property with large magnetic entropy (−ΔSm = 35.4 J kg-1 K-1 of ΔH = 7.0 T and T = 2.0 K). Remarkably, alternating current (ac) magnetic susceptibility measurement reveals that 2 exhibits typical SMM behavior with Ueff/kB = 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.