Detailed studies on complexation behaviour and mechanism of fluorescence quenching of naphthalene linked hydroxamic acid with transition metal ions by UV-visible and fluorescence spectra

The stoichiometry of the complex formation and mechanism of fluorescence quenching of compounds 1 and 2 with Fe(III), Cu(II) and Zn(II) were carried out in great detail by spectrometric and fluoromertric methods. Complexes of 1:1, 1:2 and 1:3 of metal:ligand were formed and all of them gave charge transfer absorption bands at different wavelengths. The factors effecting the complexation were found as the pH of the medium, ligand and metal ion concentrations. Also, the [metal ion]:[ligand] at a given concentration of ligand is very important in determining the stoichiometry of the complex. The quenching of the fluorescence is found to be static and due to the formation of non-fluorescent complex in the ground state. All the metal ions studied forms a 1:1 complex at 1×10−5 M concentration of the ligand 2 at pH 3, 5.6 and 6.4 for Fe(III), Cu(II) and Zn(II), respectively. Linear Stern–Volmer plots were obtained for both compounds and formation constants (log K) for the 1:1 complexes of 2 with Fe(III), Cu(II) and Zn(II) were estimated as 3.63, 3.72 and 2.45, respectively.