Bromo-complexes of cobalt(II) in acetone

Abstract

Equilibria of cobalt(II) perchlorate with lithium bromide in 0.1 mol dm^–3 LiClO₄ acetone solution have been investigated by the combination of potentiometry and spectrophotometry at 25.0 °C. An Ag–AgBr electrode gave rise to a Nernstian response in the acetone solution saturated by AgBr. Potentiometry revealed equilibria (i) and (ii), where L refers to the solvent acetone molecule. The formation constants [CoL₆][ClO₄]₂+ 2LiBr [graphic omitted] [CoBr₂L₂]+ 2LiClO₄+ 4L (i), [CoBr₂L₂]+ LiBr [graphic omitted] Li[CoBr₃L]+ L (ii) of the dibromo- and tribromo-complexes were determined as log β₂= 9.2 ± 0.4 and log K₃= 5.30 ± 0.03. By spectrophotometric measurements, equilibrium (iii) occurred at higher LiBr concentration. Li[CoBr₃L]+ LiBr [graphic omitted] Li₂[CoBr₄]+ L (iii) The formation constant of the tetrabromo-complex was determined as log K₄= 1.89 ± 0.05. The spectral data of these complexes are presented and are compared with those of other systems.