Synthesis, Structure, and Magnetism of a Family of Heterometallic {Cu(2)Ln(7)} and {Cu(4)Ln(12)} (Ln = Gd, Tb, and Dy) Complexes: The Gd Analogues Exhibiting a Large Magnetocaloric Effect.

The syntheses, structures, and magnetic properties of two heterometallic Cu-II-Ln(III) (Ln(III) = Gd, Tb, and Dy) families, utilizing triethanolamine and carboxylate ligands, are reported. The first structural motif displays a nonanuclear {Cu(2)(II)Ln(7)(III)} metallic core, while the second reveals a hexadecanuclear {Cu(4)(II)Ln(12)(III)} 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 {(Cu2Gd7III)-Gd-II} and {(Cu4Gd12III)-Gd-II} complexes, which display a large magnetocaloric effect, with entropy changes -Delta 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 {(Cu4Dy12III)-Dy-II} complex displays single-molecule magnet behavior, with an anisotropy barrier to magnetization reversal of 10.1 K.