Chloro complexes of cobalt(II) in acetone

Abstract

Equilibria of cobalt(II) perchlorate with lithium chloride in 0.1 M LiClO₄ acetone solution have been investigated by means of potentiometry and spectrophotometry at 25.0°C. By the addition of a large excess of medium salt (LiClO₄), the ionic dissociation of electrolytes are surpressed and the ion-pairs predominate in this medium. It was confirmed that AgAgCl electrode gives rise to the Nernstian response in this medium. The potentiometry reveals the formation of following chloro complexes of cobalt (II): $\text{Co(ClO}{}_4\text{)}{}_2\text{+LiCl}\text{⇌}\text{K}{}_1\text{CoCl(ClO}{}_4\text{)+LiClO}{}_4$$\text{Co(ClO}{}_4\text{)+LiCl}\text{⇌}\text{K}{}_2\text{CoCl}{}_2\text{+LiClO}{}_4$$\text{CoCl}{}_2\text{+LiCl}\text{⇌}\text{K}{}_3\text{LiCoCl}{}_3$

Successive formation constants were determined as log K₁ = 5.0 ± 0.3, log K₂ = 6.2 ± 0.3 (log β₂ = log K₁K₂ = 11.15 ± 0.03) and log K₃ = 5.97 ± 0.03. By the spectrophotometric titration at higher concentration of lithium chloride, we have the following equilibrium: $\text{LiCoCl}{}_3\text{+LiCl}\text{⇌}\text{K}{}_4\text{LiCoCl}{}_3$ with formation constant of log K₄ = 2.64 ± 0.05. Absorption spectra of these complexes are presented.