Conductance behavior of some tris(ethylenediamine)cobalt(III) complexes and their ion association in aqueous solutions

The conductance behavior of some tris(ethylenediamine)cobalt(III) complexes was studied in dilute aqueous solutions at 25°C to investigate the ion-pair formation. The thermodynamic formation constants of the ion pairs Co(en)₃]³⁺·X^– are 28 (chloride), 28 (bromide), 19 (nitrate), and 15 (perchlorate). These values were compared with theoretical values calculated by using Bjerrum's theory of ion association. The formation constant of Co(en)₃]³⁺·Cl^– was larger than that obtained from the spectrophotometric measurement in solutions containing perchlorate ion. This difference in the formation constants was explained by considering the contribution of ion association of the complex cation with perchlorate ion.