Structures, fluorescence properties and magnetic properties of a series of rhombus-shaped Ln III4 clusters: magnetocaloric effect and single-molecule-magnet behavior†
Reactions of Ln(acac)3·2H2O (Ln = SmIII (1), EuIII (2), GdIII (3), TbIII (4), DyIII (5), HoIII (6), ErIII (7)) with a bitidentate flexible ligand (HL) in an acetonitrile and dichloromethane mixture solvent result in a family of Ln4 clusters with the formula [Ln4(acac)4(μ2-OH)(L)6]·xCH3CN·yC2H5OH (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 Ln4 core. All the LnIII ion centers adopt a distorted square-antiprismatic coordination geometry. Magnetic investigations reveal that cluster 3 displays magnetic refrigeration properties with a significant entropy change (−ΔSm) of 23.37 J kg−1 K−1 (−ΔH = 7.0 T, T = 2.0 K), whereas cluster 5 shows remarkable SMM behavior with two distinct slow magnetic relaxation processes (ΔE/kB = 124.8 K and τ0 = 1.12 × 10−8 s for FR, and ΔE/kB = 39.5 K, τ0 = 6.95 × 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.