Lanthanide dimers in coordination chains constructed by sole dicarboxylate ligand for single-molecule magnet behavior and magnetocaloric effect

The solvothermal reaction of Dy(III) and Gd(III) ions with 2,5-di‑hydroxy-benzene-1,4-di-carboxylic acid (H4dhbdc) produced two new isostructural lanthanide(III) coordination chains with the general formula {[Ln2(H2dhbdc)3(H2O)8]·6H2O}n [Ln = Dy (1) and Gd (2)]. The chains consist of carboxylate-bridged dilanthanide(III) units linked by H2dhbdc2− ligands in an end-to-end bridging mode. The Dy3+ and Gd3+ ions are located in slightly distorted biaugmented trigonal prism (C2v) and triangular dodecahedron (D2d) coordination environments, respectively. Magnetic studies reveal the extremely weak antiferromagnetic interaction (J = -0.041 cm−1) between the magnetically isotropic GdIII ions in 2. The dysprosium analogue was found to exhibit single-molecule magnet (SMM) behavior with a prominent QTM effect under zero dc field, which is largely due to large single-ion magnetic anisotropy of individual Dy3+ ions and weak antiferromagnetic interaction. For the gadolinium chain, the magnetocaloric effect (MCE) was observed with a magnetic entropy change of 20.2 J kg−1 K − 1. These results demonstrate a dicarboxylate synthetic route for the preparation of coordination polymers containing dilanthanide units for SMM and MCE applications.