Structures, fluorescence properties and magnetic properties of a series of rhombus-shaped LnIII4 clusters: magnetocaloric effect and single-molecule-magnet behavior

Reactions of Ln(acac)(3)center dot 2H(2)O (Ln = Sm-III (1), Eu-III (2), Gd-III (3), Tb-III (4), Dy-III (5), Ho-III (6), Er-III (7)) with a bitidentate flexible ligand (HL) in an acetonitrile and dichloromethane mixture solvent result in a family of Ln(4) clusters with the formula [Ln(4)(acac)(4)(mu(2)-OH)(L)(6)]center dot xCH(3)CN center dot yC(2)H(5)OH (Hacac = acetylacetone, HL = 5-(4-ethylbenzylidene)-8-hydroxylquinoline). X-ray diffraction studies reveal that clusters 1-7 are isostructural and possess a rhombus-shaped tetranuclear Ln(4) core. All the Ln(III) ion centers adopt a distorted square-antiprismatic coordination geometry. Magnetic investigations reveal that cluster 3 displays magnetic refrigeration properties with a significant entropy change (-Delta S-m) of 23.37 J kg(-1) K-1 (-Delta H = 7.0 T, T = 2.0 K), whereas cluster 5 shows remarkable SMM behavior with two distinct slow magnetic relaxation processes (Delta E/k(B) = 124.8 K and tau(0) = 1.12 x 10(-8) s for FR, and Delta E/k(B) = 39.5 K, tau(0) = 6.95 x 10(-7) s for SR). Furthermore, the solid-state luminescence property indicates that clusters 1, 2, 4 and 5 display the characteristic lanthanum luminescence at room temperature.