Complexes of Zn(II) containing (o-)/(p-) carboxylato phenyl azo pentane 2,4-dione and 2,2′ bipyridine as ligands: Synthesis, characterization, colorimetric and fluorometric modulation in the presence of Ag+ ions

Abstract

Azo-enol based ligands 2-[N′-(1-acetyl-2-oxo-propylidene) hydrazino]-benzoic acid (L1H2) and 4-[N′-(1 acetyl-2 oxo-propylidene)-hydrazino]-benzoic acid (L2H2) and their complexes [Zn(L1H)2(bpy)] (1) and [Zn(L 2H)2(bpy)] (2) (where bpy = 2, 2′-bipyridine) have been synthesized and characterized using elemental analyses, spectral (FT-IR, 1H NMR, 13C NMR, electronic absorption), emission and single-crystal X-ray diffraction studies. Complexes 1 and 2 display selective chromogenic and fluorogenic responses with Ag+ ions in the presence of several other metal ions. The binding is monitored separately using UV-Vis, fluorescence and 1H NMR spectral titrations. Job's plot supports a 1:2 stoichiometry for 1 and 2 with Ag+ ions. The pH dependent "on-off" switching of fluorescence from complexes 1 and 2 have been studied. The fluorescence intensity quenches (turns-off) upon addition of OH- ions, while it enhances (turns-on) in the presence of H + ions. © 2012 Elsevier Ltd. All rights reserved.