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 {CuII 2LnIII 7} metallic core, while the second reveals a hexadecanuclear {CuII 4LnIII 12} 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 {CuII 2GdIII 7} and {CuII 4GdIII 12} complexes, which display a large magnetocaloric effect, with entropy changes -?Sm = 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 {CuII 4DyIII 12} complex displays single-molecule magnet behavior, with an anisotropy barrier to magnetization reversal of 10.1 K.