Tricarboxylate-based Gd coordination polymers exhibiting large magnetocaloric effects

Two Gd III coordination polymers with the formula [Gd(cit)(H 2 O)] ∞ ( 1 ) and [Gd(nta)(H 2 O) 2 ] ∞ ( 2 ) (H 4 cit = citric acid, H 3 nta = nitrilotriacetic acid) have been successfully prepared under hydrothermal conditions. Complex 1 exhibits a three-dimensional (3D) structure based on carboxylate-bridged layers, while complex 2 is a double-layer structure containing eight-coordinated Gd III . Magnetic investigations reveal that weak antiferromagnetic couplings between adjacent Gd III ions in both 1 and 2 with different Weiss values result in large cryogenic magnetocaloric effects. It is notable that the maximum entropy changes (−Δ S max m ) of 1 and 2 reach 31.3 J kg −1 K −1 and 32.2 J kg −1 K −1 at 2 K for a moderate field change (Δ H = 3 T), and a remarkable −Δ S max m (41.5 J kg −1 K −1 for 1 and 42.0 J kg −1 K −1 for 2 ) could be obtained for Δ H = 7 T. Hydrothermal reactions of Gd 2 O 3 and two tricarboxylates generated two carboxylate-bridged 2D/3D Gd III coordination polymers with large magnetocaloric effects.