Synthesis, Structure, and Magnetism of a Family of Heterometallic {Cu2Ln7} and {Cu4Ln12} (Ln = Gd, Tb, and Dy) Complexes: The Gd Analogues Exhibiting a Large Magnetocaloric Effect

The syntheses, structures, and magnetic properties of two heterometallic CuII–LnIII (LnIII = Gd, Tb, and Dy) families, utilizing triethanolamine and carboxylate ligands, are reported. The first structural motif displays a nonanuclear {CuII2LnIII7} metallic core, while the second reveals a hexadecanuclear {CuII4LnIII12} core. The differing nuclearities of the two families stem from the choice of carboxylic acid used in the synthesis. Magnetic studies show that the most impressive features are displayed by the {CuII2GdIII7} and {CuII4GdIII12} complexes, which display a large magnetocaloric effect, with entropy changes −ΔSm = 34.6 and 33.0 J kg–1 K–1 at T = 2.7 and 2.9 K, respectively, for a 9 T applied field change. It is also found that the {CuII4DyIII12} complex displays single-molecule magnet behavior, with an anisotropy barrier to magnetization reversal of 10.1 K.