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)2n·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; H2azdc = 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 Ln2(CO2)6n 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 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 μ1,3-COO groups. Meanwhile, the magnetic study reveals that 3 displays cryogenic magnetic refrigeration property, whereas 5 shows magnetic dynamics at low temperature.