Equivalent conductivities and ion association constants of some tris-(ethylenediamine)cobalt(III) complexes in dimethyl sulfoxide at different temperatures

The equivalent conductivities of tris-(ethylenediamine)cobalt(III) complexes, [Co(en)3]X3 (X = Cl−, Br−, I−; en = ethylenediamine) were measured as functions of temperature (288.15-328.15 T/K) and concentration (1.958 × 10− 4-10.260 × 10− 4 c/mol·dm− 3) in dimethyl sulfoxide (DMSO). Equivalent conductivity values for [Co(en)3]X3 in DMSO were varied in the order Cl− > Br− > I−. The conductivity data were analyzed by using Robinson-Stokes equations. For [Co(en)3]X3, the limiting equivalent ionic conductivities of [Co(en)3]3 + and the ion association constants (KA) of the ion pair formed between [Co(en)3]3 + with monovalent halide anions were determined in DMSO. KA values for three complex salts in DMSO were decreased in the order Cl− > Br− > I−. While KA values for [Co(en)3]Cl3 apparently increased with increase in temperature, those of [Co(en)3]Br3 and [Co(en)3]I3 slightly increased with temperature. The temperature variations of the association constants for [Co(en)3]X3 in DMSO have also been studied to get the thermodynamic functions (standard Gibbs energy, enthalpy and entropy changes).