Affinity of polypyridines towards CdII and CoII ions:: a thermodynamic and DFT study

Cd-II and Co-II complex formation with pyridine (py), 2,2'-bipyridine (bipy), 2,2'6',2"-terpyridine (terpy), 2-(aminomethyl)pyridine (amp), and bis[(2-pyridyl)methyl]amine (dpma) was studied at 298 K in the aprotic solvent dimethyl sulfoxide (DMSO) and in an ionic medium set to 0.1 mol dm(-1) with Et(4)NCiO(4) in anaerobic conditions. Potentiometric, UV/ Vis spectrophotometric, and calorimetric measurements were carried out to obtain the thermodynamic parameters of the systems investigated. Enthalpy-stabilized mononuclear MLj complexes are formed, whereas entropy changes counteract complex formation. These results are discussed in terms of different basicities, steric requirements, and solvation, of both the ligands and the resulting complexes. Density functional theory (DFT) calculations were carried out in order to obtain structural information and binding energies in vacuo. The DFT results are correlated with the solution studies. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).