There have been comparatively few studies made on the complex formation between phenolate anions and metal ions. Much of the interest has been focused on the colored complex of iron(III) phenolate and formation constants of this complex were recorded (1).
We previously reported the equilibrium data of mercury(II) and thorium(IV) complexes with phenolate ligands in aqueous solution (2-4). To obtain a more comprehensive picture of the complex formation ability of the phenolate anion with metal ions, we report in the present paper the result of our potentiometric studies on the complexation tendency of phenolate anion with divalent manganese, cobalt, nickel, and copper ions in aqueous sodium perchlorate solutions of 0.1 M ionic strength at 25.0ЊC.
The complexing reactions of phenolate ions with the first-row transition metal ions, namely Mn(II), Co(II), Ni(II), and Cu(II), do not appear to have been studied before.
EXPERIMENTAL
Chemicals
Mn(II) perchlorate was prepared by dissolving Mn(II) carbonate (Fluka purum) in perchloric acid (Merck, p.a.) and recrystallizing several times. The concentration of Mn(II) was determined by titration with EDTA using Erio-T as an indicator. Co(ClO 4 ) 2 r6H 2 O was purchased from Fluka. Analysis for Co(II) was made electrogravimetrically. Ni(II) perchlorate solution was prepared by dissolving NiCO 3 r2Ni- (OH) 2 r4H 2 O (Merck p.a.) in perchloric acid. The nickel concentration was determined gravimetrically with dimethylglyoxime. Copper(II) perchlorate solution was prepared from CuCO 3 rCu(OH) 2 (Merck p.a.) and HClO 4 . The copper content of the stock solution was determined electrogravimetrically. Sodium perchlorate was prepared by neutralizing Na 2 CO 3 (Merck p.a.) with HClO 4 . Perchloric acid solutions were prepared from HClO 4 (Merck p.a.) by dilution. They were standardized against borax. The free acid concentrations in the stock solutions were determined potentiometrically. Phenol (Merck for synthesis) was distilled in vacuum and stored in a vacuum desiccator. Titration solutions were freshly prepared for every titration series by mixing phenol solutions with standard sodium hydroxide and adjusting the ionic strength with sodium perchlorate to 0.1 M.