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

Seven lanthanide coordination polymers (CPs), [Ln(2)(azdc)(3)(DMA)(2)](n)center dot 2n(DMA) (Ln = Sm-III for 1, Eu-III for 2, Gd-III for 3, Tb-III for 4, Dy-III for 5, Ho-III for 6, Er-III for 7; H(2)azdc = 4,4'-azobenzoic acid, DMA = N,N-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 1-7 all consist of unique 1D lanthanide-carboxylate building units [Ln(2)(CO2)(6)](n) constructed from the adjacent Ln(III) cations and carboxyl groups of the H(2)azdc 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 1-7 have been investigated. The results indicate that unusual ferromagnetic coupling between adjacent Gd-III cations exists in 3, which is rarely reported in the Gd-III complexes only bridged by mu(1,3)-COO groups. Meanwhile, the magnetic study reveals that 3 displays cryogenic magnetic refrigeration property, whereas 5 shows magnetic dynamics at low temperature.