Two GdIII complexes derived from dicarboxylate ligands as cryogenic magnetorefrigerants

Abstract

Two Gd^III complexes, namely [Gd₂(OH)₂(oda)₂(H₂O)₄]_∞ (1) and {[Gd(fum)(ox)_0.5(H₂O)₂]·2H₂O}_∞ (2) (H₂oda = oxydiacetic acid, H₂fum = fumaric acid and H₂ox = oxalic acid), have been constructed via hydrothermal reactions. Complex 1 has a one-dimensional (1D) chain structure based on hydroxyl-bridged Gd₂O₂ cores, while complex 2 exhibits a three-dimensional (3D) framework consisting of Gd₆ macrocycles, and can also be seen as a 3D layer-pillar structure with intersected channels occupied by guest water. Magnetic studies indicate that weak antiferromagnetic and ferromagnetic interactions exist between adjacent Gd^III ions in 1 and 2, which display large magnetocaloric effects with −ΔS^max_m = 43.3 and 37.1 J kg⁻¹ K⁻¹ for ΔH = 7 T, respectively. Notably, the maximum entropy changes (−ΔS^max_m) of 1 and 2 reach 29.9 and 28.5 J kg⁻¹ K⁻¹, respectively, at 2 K for a moderate field change (ΔH = 3 T). Therefore, 1 and 2 could be regarded as potential magnetorefrigerants for low-temperature applications.