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]n·2n(DMA) (Ln = SmIII for 1, EuIII for 2, GdIII for 3, TbIII for 4, DyIII for 5, HoIII for 6, ErIII 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)6]n constructed
from the adjacent LnIII cations and carboxyl groups of
the H2azdc ligands, which can further generate 3D frameworks
with “fsy”-type topological structures via the link
of azdc2–. Furthermore, variable-temperature magnetic
susceptibility measurements of 1–7 have been investigated. The results indicate that unusual ferromagnetic
coupling between adjacent GdIII cations exists in 3, which is rarely reported in the GdIII 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.