Low-dimensional carboxylate-bridged Gd(III) 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] Gd(III)-OH ladders, but with different crystallographically independent Gd(III) ions, whilst the structures of compounds 3 and 4 were composed of [Gd4(μ3-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 Gd-O-Gd angles, whereas ferromagnetic coupling occurred in compound 4, in which the Gd-O-Gd 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 (-ΔS(m)(max)=43.6 J kg(-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 θ) between Gd(III) ions resulted in a larger MCE for the Gd(III) complexes.