Molecular assemblies from linear-shaped Ln4 clusters to Ln8 clusters using different β-diketonates: disparate magnetocaloric effects and single-molecule magnet behaviours

Abstract

A series of tetranuclear lanthanide-based clusters [Ln₄(dbm)₆(L)₂(CH₃OH)₄]·2CH₃OH (Ln(III) = Gd (1), Dy (2), and Ho (3); H₃L = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-2,3-dihydroxybenzaldehyde, Hdbm = dibenzoylmethane) and octanuclear lanthanide-based clusters [Ln₈(HL)₁₀(CH₃O)₄(CH₃OH)₂]·6CH₃OH (Ln(III) = Gd (4), Dy (5)) were assembled using a polydentate Schiff-base ligand H₃L and two different β-diketone salts via a solvothermal method, and their structures and magnetic properties have been characterized. Interestingly, β-diketones play an important role in assembling and affecting the structures of Ln₄ to Ln₈ clusters. This is the first use of β-diketone to affect the structures of polynuclear Ln(III)-based clusters from linear-shaped Ln₄ clusters to Ln₈ clusters. Magnetic studies revealed that antiferromagnetic interactions exist in clusters 1-Gd₄ and 4-Gd₈. More importantly, clusters 1-Gd₄ and 4-Gd₈ display significant cryogenic magnetic refrigeration properties (−ΔS_m = 24.88 J kg⁻¹ K⁻¹ for 1-Gd₄ and −ΔS_m = 32.52 J kg⁻¹ K⁻¹ for 4-Gd₈); the results show that cluster 4-Gd₈ exhibits a larger magnetocaloric effect than 1-Gd₄. Cluster 2-Dy₄ shows remarkable single-molecule magnet (SMM) behavior (ΔE/k_B = 67.5 K and τ₀ = 3.06 × 10⁻⁷ s) under a zero dc field, and 5-Dy₈ exhibits a field-induced SMM-like behavior (ΔE/k_B = 39.83 K and τ₀ = 2.12 × 10⁻⁷ s) under a 5000 Oe dc field.