Zn(II)-based metal-organic frameworksderived from dicarboxylate ligand and N-donor ligands as luminescent sensors for selective detection of picric acid

The reactions of Zn(II) salts with 4, 4ʹ-(1, 3-phenylenebis (methyleneoxy)) dibenzoic acid(pbd), 1,4-bis(imidazol-1-yl)butane (bib) and 1,10-phenanthroline (1,10-phen) co-ligands afforded two coordination polymers, [Zn(pbd)(bib)] (1) and [Zn(pbd)(1,10-phen)·4H2O] (2). The pbdcaptures the in situ generated scission product of C-O bondwith 4-(3-(hydroxymethyl)benzyloxy)benzoic acid (hbb). A new polymer of [Zn(hbb)(4,4′-bipy)](3) was also synthesized using the rigid N-donor ligand of 4,4′-bipyridine (4,4′-bpy). These polymers were characterized by IR spectroscopy, and Thermogravimetric analysis and further their structures were determined by single-crystal X-ray diffraction analysis. Compound 1 has 2D covalent network. 2 and 3 show 1D chains, which can be further interlinked into 2D supramolecular layer through π─π packing and hydrogen bonded interactions, respectively. The results indicated that 1 displayed good sensing property against most of the nitroaromatic compounds (NACs) by the decrease in its luminescent intensity. With 2,4,6-trinitrophenol (picric acid) Ksv value of 2.93 × 103 M−1 and limit of detection (LOD) of 1.24  ppm was observed. The plausible mechanism of the decline in the luminescent intensity of 1 in presence of NACs has been addressed with the help of theoretical calculations.