A detailed spectrophotometric investigation of the stability constants of [PdCln(OH)4-n]2- and [PdBrn(OH)4-n]2- (n = 0-4)

Abstract

Complex formation of mixed palladium (II) chloro-hydroxo and palladium(II) bromo-hydroxo complexes have been investigated employing spectrophotometry at 25 °C and an ionic strength of 1.0 M. Hyperquad Simulation and Speciation (HySS) was employed to determine the ideal titration conditions and an autotitrator (equipped with a flow-through cell) was used to accurately vary the pH over 80 and 90 intervals respectively. The stability constants (log βn) for the mixed chloro-hydroxo complexes [PdCl4-n(OH)n]2− (n = 0–4), are: log β1 = 18.36, log β2 = 23.21, log β3 = 26.91 and log β4 = 29.68. These newly obtained values represent a more accurate representation for the stability constants of the mixed palladium(II) chloro-hydroxo speciation. The same experimental procedure was employed to calculate, for the first time, the stepwise stability constants of the palladium(II) bromo-hydroxo system, [PdBr4-n(OH)n]2− (n = 0–4), i.e. log β1 = 18.73, log β2 = 22.25, log β3 = 25.58 and log β4 = 28.47. Molar absorption spectra for all the complexes in question have been obtained. For both systems, complete Pourbaix diagrams were constructed from the new speciation data showing the predominant species for each system