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 Gd 2 O 3 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 [Gd 4 (μ 3 ‐OH) 2 (piv) 8 (H 2 O) 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 (−Δ S 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.