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)₃·2H₂O (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 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 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 (−ΔS_m) 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/k_B = 124.8 K and τ₀ = 1.12 × 10⁻⁸ s for FR, and ΔE/k_B = 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. [ABSTRACT FROM AUTHOR]