1Department of Chemistry, Shiraz University, Zip code 71454, Shiraz, I.R. IRAN
2Department of Chemistry, Razi University, Zip code 67145, Kermanshah, I.R. IRAN
The complexation reactions between methylthymol blue (MTB) and Co2+, Ni2+, Cu2+, Zn2+ and Pb2+ ions have been studied in different water-methanol mixtures at pH 4.45 and 25 °C by a spectrophotometric technique. The stepwise stability constants of the resulting 1:1 and 2:1 (metal ion to ligand) complexes were determined from the absorbance-mole ratio data. It was found that the overall stability constants of the complexes formed increase in the order Zn2+<Co2+<Pb2+<Ni2+<Cu2+ for all solvent mixtures studied. There is an inverse relationship between the overall stability of the complexes and amount of water in the mixed solvent. A linear relationship was observed between log b2 of the complexes and the mole fraction of methanol in the solvent mixture.