Multifunctional Applications of Self‐Assembled Novel Ln ^III (Dy ^III and Gd ^III ) Isotructural Nanoclusters: Single‐Molecule Magnetism and MRI Contrast Agent

Rare earth clusters have demonstrated promising application prospects, owing to their distinctive topological structures and electronic configurations. Herein, two novel Ln^III (Ln = Dy^III and Gd^III) clusters were synthesized using 2-hydroxy-1-naphthaldehyde and 1,1-di(hydroxymethyl)ethylamine, along with Dy(ClO₄)₃·10H₂O and Gd(ClO₄)₃·10H₂O, respectively named as [Dy₅(L)₁₂(μ₃-OH)₂(H₂O)₂]Cl·4EtOH·2CH₃CN·5H₂O (1) and [Gd₅(L)₁₂(μ₃-OH)₂(H₂O)₂]Cl·5EtOH·5CH₃CN·11H₂O (2). The single crystal X-ray diffraction results indicated that clusters 1 and 2 possessed highly stable co-vertex double triangular metal skeletons, in which the Ln^III spin centers form a triangular [Ln₃O] cluster via μ₃-OH. Magnetic studies revealed that cluster 1 exhibited the characteristic slow relaxation property associated with single-molecule magnets (SMMs), with an effective energy barrier (U_eff/k_B) of 1.48 and 4.76 K under 0 and 2000 Oe DC field, respectively. In contrast, cluster 2 showed low-temperature magnetic refrigeration characteristics (maximum -ΔS_m = 9.76 J kg^-1 K^-1, ΔH = 5 T at 2.0 K). In addition, cluster 2 exhibited an excellent longitudinal relaxation rate (r₁) with 2.74 mm^-1s^-1 at 0.5 T and a relatively suitable r₂/r₁ value (1.12), indicating that it can serve as a typical T₁-type magnetic resonance contrast agent.