Copper(II) and nickel(II) chelates with some substituted 4-pyrazolone dyes in dioxane-water medium. Structure stability relationships

Abstract

Acid dissociation constants, pK i of a series of 4- pyrazolones (la-f) has been determined potentiometrically in 70% (v/v) dioxane-water media at 30 °C and 0.1 M ionic strength. The stability constants, logβ 1 and logβ 2 of their copper(II) and Ni(II) chelates have also been determined. The effects of substituents on the ligand dissociation were discussed. Both values of pK i and logβ n were linearly correlated with Hammett substituent, σ. The equations of the straight lines obtained are: pK i = 8.758 − 1.911σ (r = 1); logβ 1 Cu(II) = 8.25 − 0.99σ (r = 0.980); logβ 2 Cu(II) = 15.131−1.82 σ(r = 0.999); logβ 1Ni(II) = 5.931− 1.07σ (r = 0.899); logβ 2 Ni(II) = 12.53 − 1.28σ(r = 0.911).