Construction of a family of Ln3 clusters using multidentate Schiff base and β-diketonate ligands: fluorescence properties, magnetocaloric effect and slow magnetic relaxation

Abstract

A family of μ-O_{acylhydrazone}-bridged Ln₃ clusters, [Ln₃(dbm)₅(HL)₂]·x[solvent] (Ln = Nd (1), Sm (2), Gd (3), Tb (4), Dy (5), Ho (6), and Er (7), H₃L = N′-(2-hydroxybenzylidene)-6-(hydroxymethyl)picolinohydrazide, and Hdbm = dibenzoylmethane), was successfully obtained by using a multidentate hydrazone ligand and lanthanide β-diketone salts via a solvothermal method. The seven Ln₃ clusters were characterized by performing infrared spectroscopy (IR), elemental analysis (EA), thermogravimetric analysis (TGA), UV-Vis spectroscopy and single-crystal X-ray diffraction. Structural analyses showed clusters 1–7 to be isostructural and to mainly contain three Ln(III) ions connected through four μ-O_hydrazone bridges. The magnetism investigations indicated showed cluster 3 displaying cryogenic magnetic refrigeration with a −ΔS_m of 20.60 J K⁻¹ kg⁻¹ (T = 2.0 K, ΔH = 7.0 T); while cluster 5 showed slow magnetic relaxation with a ΔE/k_B of 20.47 K and τ₀ of 1.4 × 10⁻⁸ s. Moreover, solid-state fluorescence analyses showed clusters 2, 4 and 5 displaying the characteristic lanthanum luminescence at room temperature.