Spectrophotometric Studies of Dioxo‐Complexes of Quadrivalent Metals. I. Complexes of Zirconium and Hafnium with Pyrogallolsulfonephthalein

Abstract Pyrogallolsulfonephthalein and its complexes with zirconium and hafnium were spectrophotometrically studied in HClO4 and NaClO4 solutions of various pH's. An absorption maximum at 472 mμ has been found for pyrogallolsulfonephthalein at pH 1.0 and 1.5. It shifts to 518 and 520mμ in the presence of zirconium at pH 1.0 and hafnium at pH 1.5, respectively. The mole ratios of both metals to the dye have been found to be 1:1, and the apparent instability constants of the complexes are estimated as 1.34×10−5 for the former and 7.06×10−6 for the latter.