Structures and magnetic properties of novel Ln(iii)-based pentanuclear clusters: magnetic refrigeration and single-molecule magnet behavior

Abstract

Six new and novel polynuclear Ln^III₅ clusters, formulated as [Ln₅(L)₄(acac)₇]·solvents (Ln(III) = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5) and Ho (6), Hacac = acetylacetone, and H₂L = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-5-hydroxymethyl-2-furancarboxylic acid) have been successfully obtained through the reaction of a polydentate Schiff base ligand (H₂L) and Ln(acac)₃·2H₂O. Single crystal X-ray diffraction data indicate that clusters 1–6 are isostructural and their central Ln(III) ions have a Ln(III)₅ chain arrangement. Magnetic property investigations show that the Gd(III)-based cluster (3) exhibits a significant and larger MCE with the maximum −ΔS_m value of 34.02 J kg⁻¹ K⁻¹ (ΔH = 7.0 T and T = 2.0 K). Alternating current (ac) susceptibility measurements of the Dy(III)-based cluster (5) display remarkable slow magnetic relaxation behaviors at zero applied direct current (dc) magnetic field (ΔE/k_B = 17.47 K and τ₀ = 1.52 × 10⁻⁶ s). Furthermore, studies on the solid-state fluorescence properties show that clusters 2, 4, and 5 display the characteristic lanthanum luminescence at room temperature.