A new 3D luminescent Zn(ii)-organic framework containing a quinoline-2,6-dicarboxylate linker for the highly selective sensing of Fe(iii) ions

A new 3D zinc-organic framework [Zn(QDA)]center dot 0.5H(2)O center dot 0.7DMF (1, H(2)QDA = quinoline-2,6-dicarboxylic acid, DMF = N, N-dimethylformamide) was synthesized under solvothermal conditions. The single crystal X-ray diffraction analysis reveals that the 3D framework structure of 1 has a PtS topology and contains Zn (II) ions having distorted square pyramidal geometry with ZnO4N configuration. The phase purity of the bulk sample was characterized by X-ray powder diffraction (XRPD), thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy. The as-synthesized sample (1) was activated by stirring with acetone for 24 h, followed by heating under vacuum for 24 h at 120 degrees C. The TGA experiment indicated that both 1 and its activated form (1') are stable up to 380 degrees C. The crystalline structure of the compound was retained after immersion in water, 1 M HCl, acetic acid and NaOH (at pH = 10) solutions. Compound 1' exhibited very quick fluorescence quenching response after the addition of Fe3+ solution. This quenching was not affected by the presence of other competitive metal cations. A very low detection limit of 9.2 ppb was observed for Fe3+ ions, which is among the lowest values documented in the literature for MOF based fluorescent probes. Both fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET) processes play major roles in the selective detection of Fe3+ ions. The recyclability experiment suggested that 1' can be used for the long-term detection of Fe3+ ions.