Low-Dimensional Carboxylate-Bridged GdIII Complexes for Magnetic Refrigeration

Four carboxylate-bridged Gd-III complexes (1-4) with 1D/2D structures have been synthesized by using the hydrothermal reaction of Gd2O3 with various carboxylate ligands. Compounds 1 and 2 contained the same [2n] (GdOH)-O-III ladders, but with different crystallographically independent Gd-III ions, whilst the structures of compounds 3 and 4 were composed of [Gd-4((3)-OH)(2)(piv)(8)(H2O)(2)](2+) units and 1D ladder Gd-III chains, respectively. Antiferromagnetic interactions occurred in compounds 1-3, owing to their small GdOGd angles, whereas ferromagnetic coupling occurred in compound 4, in which the GdOGd angles were larger. These complexes exhibited a distinct magnetocaloric effect (MCE), which was affected by their different magnetic densities and exchange interactions. Among these compounds, complex 4 presented the largest MCE (-S-m(max)=43.6Jkg(-1)K(-1)), the lowest M-w/N-Gd ratio (the highest magnetic density), and weak ferromagnetic coupling. Therefore, a lower M-w/N-Gd ratio and weaker exchange interactions (a smaller absolute value of ) between Gd-III ions resulted in a larger MCE for the Gd-III complexes.