Formation and two-phase distribution equilibria of cobalt(II) and zinc(II) complexes with β-diketones in several solvent extraction systems

Abstract

The equilibrium constants for the complex formation of cobalt(II) and zinc(II) with several β-diketones in 1M sodium perchlorate solution ( β n ), the two-phase distribution constants of the bis-chelates of these metals between carbon tetrachloride and the above aqueous solution ( Kdm), and the adduct formation of the bis-chelates with trioctylphosphine oxide (TOPO) in the organic phase ( β n( org) ) have been determined at 25°C. The distribution constants of the bis-zinc(II) chelates were also determined when the solvent was hexane, chloroform or benzene. The weaker the acidity of the ligand the higher the β n value for these complexes. The relationship, log Kdm = 2 log Kd + C, where Kd is the distribution constant of the extractant is obeyed for each of the zinc(II) chelates when the solvent is different. The Kdm values of the metal chelates with the same ligand are always lower for cobalt(II) than for zinc(II), and among the series of bis-chelates of the same metal ion, there is a tendency for β n( org) of TOPO adducts to be higher when the β 2 is lower, but the stability order of the adducts of a set of cobalt(II) and zinc(II) chelates with the same β-diketone is not always the same.