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

Abstract 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(ClO 4 ) 3 ·10H 2 O and Gd(ClO 4 ) 3 ·10H 2 O, respectively named as [Dy 5 (L) 12 ( μ 3 ‐OH) 2 (H 2 O) 2 ]Cl·4EtOH·2CH 3 CN·5H 2 O ( 1 ) and [Gd 5 (L) 12 ( μ 3 ‐OH) 2 (H 2 O) 2 ]Cl·5EtOH·5CH 3 CN·11H 2 O ( 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 [Ln 3 O] cluster via μ 3 ‐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 ‐Δ S 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 ( r 1 ) with 2.74 m m −1 s −1 at 0.5 T and a relatively suitable r 2 / r 1 value (1.12), indicating that it can serve as a typical T 1 ‐type magnetic resonance contrast agent.