Spectrophotometric Study of Cobalt, Nickel, Copper, Zinc and Lead Complexes with Methylthymol Blue in Binary Water-Methanol Mixtures

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+2+2+2+2+ 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.