‘Windmill’-shaped Ln III4 (LnIII = Gd and Dy) clusters: magnetocaloric effect and single-molecule-magnet behavior

Abstract

Two new tetranuclear lanthanide clusters with the formula [Ln₄(L)₄(μ₂-CH₃O)₄]·4CH₃OH·xC₂H₅OH (Ln^III = Gd (1) and Dy (2), H₂L = N′-(4-diethylamino-2-hydroxybenzylidene)-6-(hydroxymethyl)picolinohydrazide, x = 0 for 1 and x = 4 for 2) were assembled by using a polydentate ligand (H₂L) reacting with β-diketonate salts (Ln(acac)₃·2H₂O, Ln^III = Gd (1) and Dy (2)). Single-crystal X-ray structures reveal that clusters 1 and 2 are mainly composed of four Ln^III ions that are interconnected through eight μ₂-O bridging oxygen atoms, and the Ln₄ clusters show a ‘windmill’-shaped arrangement. The magnetic investigations reveal that cluster 1 displays a cryogenic magnetic refrigeration property with a large magnetic entropy (−ΔS_m = 29.0 J kg⁻¹ K⁻¹, ΔH = 7.0 T and T = 2.0 K); meanwhile, alternating current (ac) magnetic susceptibility measurement reveals that 2 exhibits typical SMM behavior with a U_eff/k_B of 42.4 K and pre-exponential factor τ₀ = 1.2 × 10⁻⁶ s.