Structures and magnetic properties of novel Ln(III)-based pentanuclear clusters: magnetic refrigeration and single-molecule magnet behavior
Six new and novel polynuclear LnIII5 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 indicate that clusters 1-6 are isostructural and the central Ln(III) ions of them are Ln(III)5 chain arrangement. Magnetic properties investigations show that the Gd(III)-based cluster (3) exhibit significant and larger MCE with the maximum −ΔSm 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) displays remarkable slow magnetic relaxation behaviors at zero applied direct current (dc) magnetic field (ΔE/kB = 17.47 K and τ0 = 1.52 ×10-6 s). Furthermore, the solid-state fluorescent properties studies show that clusters 2, 4, and 5 display the characteristic lanthanum luminescence at room temperature.