Biphenyltetracarboxylate-Based Luminescent Metal-Orgainc Framework for Sensing of 2,6-Dipicolinic Acid and Cr(VI) Oxo-Anions

Rational design of metal-organic frameworks (MOFs) as luminescent sensors, has attracted great interest in recent years. 2,6-dipicolinic acid (DPA) is the specific biomarker of Bacillus anthracis, Cr(VI) oxo-anions are toxic ions in environmental water, and the detection of DPA and Cr(VI) oxo-anions is of great significance. Herein, a new three-dimensional (3D) Cd(II) MOF, {[Cd₂(bpda)(1,4-bbix)_0.5(H₂O)₄]·H₂O}_n (1) (H₄bpda = 2,3,3′,4′-biphenyltetracarboxylic acid, 1,4-bbix = 1,4-bis(benzimidazol-1-yl-methyl)benzene) has been synthesized and characterized. Its crystal structure is a 3D framework, which presents a trinodal (3,3,5)-connected topology with the point symbol of (4²·6)(6²·8)(4²·6²·8⁴·10²). 1 shows excellent luminescence and stability in water, which was explored as luminescent sensor for detection of DPA, CrO₄^2- and Cr₂O₇^2- in aqueous solutions via luminescence quenching effect. The detection limits of 1 toward DPA, CrO₄^2- and Cr₂O₇^2- are 0.90, 0.53 and 0.41 μM, respectively. Furthermore, 1 also can serve as luminescent sensor to detect DPA in serum and Cr(VI) oxo-anions in river water. The quenching mechanisms were studied by theoretical calculations, PXRD, UV-vis spectra and luminescent lifetimes. The luminescent film of 1 was prepared for the visual detection of DPA, CrO₄^2- and Cr₂O₇^2-. This work presents an effective Cd(II) MOF as the functional platform for sensing of DPA, CrO₄^2- and Cr₂O₇^2- in aqueous solution.