Lanthanide-based bis-(3,5-dicarboxy-phenyl)terephthalamide metal–organic frameworks: slow relaxation of magnetization and detection of trace Fe2+ and Fe3+

Abstract

Solvothermal reactions of flexible aromatic linker bis(3,5-dicarboxyphenyl)terephthalamide (H₄BDPT) with dysprosium and samarium salts yield two Ln-based metal–organic frameworks {[Dy₂(BDPT)_1.5(DMF)₄]·H₂O}_n (1) and [Sm₂(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 χ_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 τ₀ 5.0 × 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 × 10⁻⁷ and 2.14 × 10⁻⁷ M⁻¹ for Fe²⁺, respectively.