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

Two new and interesting polynuclear lanthanide clusters, namely, [Ln(6)(acac)(4)(HL)(2)(THAM)(4)(CH3COCH3)(2)]center dot 2CH(3)OH (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 beta-diketonate salts (Ln(acac)(3)center dot 2H(2)O, 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 Ln(3) triangles via mu(3)-O and mu(2)-O atoms. The magnetic investigations reveal that 1 displays cryogenic magnetic refrigeration properties with large magnetic entropy (-Delta S-m = 35.4 J kg(-1) K-1 with Delta H = 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 tau(0) = 1.5 x 10(-6) s. It is one of the rare polynuclear Dy-6 SMMs under zero dc field.