Novel luminescent metal–organic frameworks based on rigid carboxylate ligands for highly selective sensing of Fe3+ ions

Abstract

Four three-dimensional (3D) luminescent metal–organic frameworks (MOFs), Zn₂(HL₁)(H₂O)_0.8 (1), Cd₂(L₁)(DMF)₂ (2), [Zn₃(HL₂)₂]·[(CH₃)₂NH₂]₄ (3), and [Cd₃(L₂)₂]·[(CH₃)₂NH₂]₆ (4) (H₅L₁ = 3,5-di(3′5′-dicarboxyphenyl)benzoic acid, H₆L₂ = 3,4-di(3,5-dicarboxyphenyl)phthalic acid, DMF = N,N-dimethylformamide), have been successfully assembled based on rigid carboxylate ligands. The four compounds have been characterized by elemental analysis, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), single-crystal X-ray diffraction, powder X-ray diffraction (PXRD) and fluorescence spectroscopy. Compound 1 is a (5,5)-connected 3D framework with a {4⁵·6⁵} topology. Compound 2 possesses a (5,5)-connected 3D framework with a {4⁷·6³} topology. Compounds 3 and 4 display a (4,4,6)-connected 3D framework with a {4²·6⁴}₂{4⁴·6¹¹}₂{4⁴·6²} topology. Remarkably, the four presented compounds show luminescence changes in the presence of metal ions. Interestingly, all of them exhibit highly selective sensing of Fe³⁺ ions and the luminescence is quenched in a 1.1 × 10⁻³ M DMF solution of Fe³⁺ ions. Moreover, the four compounds possess reasonable recyclability and reproducibility of luminescence after regeneration. The exceptional sensitivity and reusability of the four compounds make them excellent Fe³⁺ sensors in the future.