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

Pyrogallolsulfonephthalein and its complexes with zirconium and hafnium were spectrophotometrically studied in HClO 4 and NaClO 4 solutions of various p H's. An absorption maximum at 472 mμ has been found for pyrogallolsulfonephthalein at p H 1.0 and 1.5. It shifts to 518 and 520mμ in the presence of zirconium at p H 1.0 and hafnium at p H 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.