Thermodynamic studies on the complexation of cobalt(II) with nitrogen donor ligands in dimethyl sulfoxide

Co(II) complex formation with the N-donor ligands n-butylamine (n-but), diethylenetriamine (dien), N,N″-dimethyldiethylenetriamine (dmdien) and N,N,N′,N″,N″-pentamethyldiethylenetriamine (pmdien) has been studied at 298 K in the aprotic solvent dimethyl sulfoxide (dmso) in an ionic medium set to 0.1 mol dm−3 with NEt4ClO4 in anaerobic conditions. Potentiometric, spectrophotometric and calorimetric measurements have been carried out to obtain the thermodynamic parameters for the systems investigated. Only mononuclear CoLj 2+ complexes are formed (j=1–3 for n-but; j=1, 2 for dien and dmdien; j=1 for pmdien) where the triamines act prevalently as terdentate agents. All the complexes are enthalpy stabilized whereas the entropy changes counteract the complex formation. The results are discussed in term of different basicities and steric requirements of both the ligands and the complexes formed. Preliminary information on the different affinities of the complexes for dioxygen is reported.