Semi-xylenol orange complexes with bivalent metal ions

Abstract

Potentiometric, spectrophotometric and ESR spectrometric investigations have been applied to several bivalent metal complexes with Semi-Xylenol Orange (SXO or H 4SXO) in aqueous solutions. The metal ions were Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II). The stoichiometries of the complexes, the formation constants and UV data for all the metal complexes and ESR parameters for Cu(II) were determined. The species MHSXO − for Co(II), Ni(II), Cu(II), Zn(II), Hg(II) and Pb(II), MSXO 2− for Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II), and M(OH)SXO 3− for Cu(II) were found to be formed. The λ max of the MSXO 2−, due to a π−π ∗ transition in the SXO molecule, has a linear relationship with the proton dissociation constant of each metal aquo ion and the shift in λ max has been explained using the concept of the hard and soft character of the metal ion. CuSXO 2− was found to be relatively unstable compared with the other metal ions. Its instability may be explained because the tetradentate ligand SXO becomes tridentate in the Cu(II) complex as the result of the axially distortion of the central Cu(II).