Spectrophotometric Determination of the Stability Constants of Co(II) and DPKBH (DI-2-Pyridyl Ketone Benzoylhydrazone)

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Abstract
In order to have more information about the thermodynamic properties of the complexes formed by Cobalt(II) and DPKBH (di-2-pyridyl ketone benzoylhydrazone) and for the development of speciation methods for cobalt, the respective stepwise formation constants were determined in ethanolic solution 50% (V/V), at pH 5.3 and 25.0°C. The spectrophotometric method of corresponding solutions was used and the following overall formation constants were obtained: β1 = 5.305 × 106 M−1 and β2 = 8.476 × 1010 M−2. The molar absorptivities of the 1:1 (ε1) and 1:2 (ε2) complexes (Co(II):DPKBH) were determined to be 4.475 × 10 and 2.994 × 10 (M−1cm−1), respectively. The calculated distribution diagram shows the percentage of the species at equilibrium as a function of the free DPKBH concentration.