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

Three new Ln(4) clusters based on a bidentate Schiff base ligand having formulae [Ln(4)((3)-OH)(2)L-6(acac)(4)]xCH(3)CN (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 -S-m = 18.85 J kg(-1) K-1 (H = 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 (E/k(B)) of 79.15 K and a pre-exponential factor (0) = 5.82 x 10(-8) s.