Lanthanide-Based Bis-(3,5-Dicarboxy-Phenyl)Terephthalamide Metal-Organic Frameworks: Slow Relaxation Of Magnetization And Detection Of Trace Fe2+ And Fe3+

Solvothermal reactions of flexible aromatic linker bis(3,5-dicarboxyphenyl)terephthalamide (H4BDPT) with dysprosium and samarium salts yield two Ln-based metal-organic frameworks {[Dy-2(BDPT)(1.5)(DMF)(4)]center dot H2O}(n) (1) and [Sm-2(BDPT)(1.5)(DMF)(4)](n) (2) with inserted acylamide groups. Both 1 and 2 possess a 3D open framework built from 6-connecting Ln2 clusters and 4-connecting tetracarboxylate ligands. There are small 1-D helical channels in the structure occupying 29.8% of the framework. Magnetic measurements reveal that compound 1 exhibits weak antiferromagnetic interactions between Dy3+ ions and a distinct slow relaxation phenomenon. The frequency-dependent ac susceptibility results reveal that 1 exhibits an chi(M)'' ac signal with observable maxima under 1500 Oe, indicating the signature of SMM behavior with the anisotropic barrier of 25 K and the pre-exponential factor tau(0) 5.0 x 10(-7) s. Furthermore, both 1 and 2 serve as fluorescent probes for selectively detecting trace Fe2+ and Fe3+ through the luminescence emission quenching effect, with the detection limit of 1.03 x 10(-7) and 2.14 x 10(-7) M-1 for Fe2+, respectively.