Butterfly-like Heteronuclear 3d–4f Metal Clusters: Synthesis, Structures, Magnetic Properties, and Magnetocaloric Effect

This study describes the self-assembled synthesis, characterization, and structural features of two new heterometallic Fe6Ln clusters, [Fe6Ln(μ3-OH)2(mdea)6(N3)6(NO3)] (Ln = Y (1), Gd (2); mdeaH2 = N-methyldiethanolamine). The obtained compounds possess a unique crystalline structure with a vertex-sharing butterfly-like Fe3LnFe3 motif and a rare type of 2,3,4M7-1 topology. The compounds show a new prototype structure with a distinctive arrangement of a lanthanide center between the Fe3 triangles. Magnetic properties of the obtained clusters were investigated in detail. In 1, the best fit through a spin Hamiltonian to the experimental data of both magnetic susceptibility and magnetization curves gave J values ranging from −5.5 to −11.1 cm–1. In 2, these values vary from −18.0 to −31.5 cm–1. The cluster 2 also showed a magnetocaloric effect (MCE) with a −ΔSm value of 10.6 J kg–1 K–1 (16.3 J mol–1 K–1) at 2.0 K. This effect is superior to that of other metallacrown compounds (with one Gd inside of an antiferromagnetic matrix of iron centers). The obtained compounds bring a new example of heptametallic clusters into a family of heteronuclear iron(III)-lanthanide derivatives with notable structural characteristics and magnetic behavior. © 2021 American Chemical Society