Lanthanide Coordination Polymers with “fsy-type” Topology Based on 4,4′-Azobenzoic Acid: Syntheses, Crystal Structures, and Magnetic Properties

Seven lanthanide coordination polymers (CPs), [Ln₂(azdc)₃­(DMA)₂]_<i>n</i>·2<i>n</i>(DMA) (Ln = Sm^III for <b>1</b>, Eu^III for <b>2</b>, Gd^III for <b>3</b>, Tb^III for <b>4</b>, Dy^III for <b>5</b>, Ho^III for <b>6</b>, Er^III for <b>7</b>; H₂azdc = 4,4′-azobenzoic acid, DMA = <i>N</i>,<i>N</i>-dimethylacetamide), have been successfully prepared with high yields via solvothermal methods and further studied by elemental analyses (EA), powder X-ray diffraction (PXRD), UV–vis spectra, photoluminescent spectra, thermogravimetric analyses (TGA), variable-temperature in situ PXRD analyses, and single-crystal X-ray diffraction. CPs <b>1</b>–<b>7</b> all consist of unique 1D lanthanide-carboxylate building units [Ln₂(CO₂)₆]_<i>n</i> constructed from the adjacent Ln^III cations and carboxyl groups of the H₂azdc ligands, which can further generate 3D frameworks with “fsy”-type topological structures via the link of azdc^2–. Furthermore, variable-temperature magnetic susceptibility measurements of <b>1</b>–<b>7</b> have been investigated. The results indicate that unusual ferromagnetic coupling between adjacent Gd^III cations exists in <b>3</b>, which is rarely reported in the Gd^III complexes only bridged by μ_1,3-COO groups. Meanwhile, the magnetic study reveals that <b>3</b> displays cryogenic magnetic refrigeration property, whereas <b>5</b> shows magnetic dynamics at low temperature