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 Fe(6)Ln clusters, [Fe(6)Ln(mu(3)-OH)(2)(mdea)(6)(N-3)(6)(NO3)] (Ln = Y (1), Gd (2); mdeaH(2) = N-methyldiethanolamine). The obtained compounds possess a unique crystalline structure with a vertex-sharing butterfly-like Fe(3)LnFe(3) 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 Fe-3 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 -Delta S-m 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.