Enhanced Magnetocaloric Effect and Single-Molecule Magnet Behavior in a Series of Sulfur-Containing Ligand-Based Ln9 Clusters (Ln = Gd, Tb, and Dy)

As an important branch of lanthanide-based complexes, clusters show unique properties in magnetocaloric effect (MCE) and single-molecule magnets (SMMs) using O/N ligands, while research on heavy p-block elements (e.g., S atom) with larger atomic radii and more diffuse p valence orbitals as coordinating atoms remains relatively scarce. Herein, using the sulfur-containing ligand of 2-pyridinethiol 1-oxide (HL), we successfully synthesized a series of hourglass-like Ln9 clusters [Ln9(L)17(μ3-OH)9(μ4-OH)]·nH2O (1: Ln = Gd, n = 3; 2: Ln = Tb, n = 3; 3: Ln = Dy, n = 1). Magnetic data analysis reveals that cluster 1 shows a significant MCE, with the entropy change (−ΔSm) reaching a maximum of 34.41 J kg−1 K−1 at 2 K under ΔH = 7 T. Cluster 3, meanwhile, exhibits distinct frequency- and temperature-dependent behavior, indicating its SMM characteristics. Interestingly, despite possessing the highest molar mass among reported Gd9 clusters with MCE, 1 exhibits a competitive −ΔSm value, highlighting the critical role of sulfur-containing ligand on the structure and even exchange interactions. This work offers new insights into synthesizing high-performance MCE materials and understanding magneto-structural relationships.