Thermodynamics of complex formation of silver(I), cadmium(II) and cobalt(II) with open-chain polyamines in dimethyl sulfoxide and molecular dioxygen binding to cobalt(II) complexes

Ag-I, Cd-II and Co-II complex formation with the primary And tertiary tetraamines 1,4,7,10-tetraazadecane (trien) and 1,1,4,7,10,10-hexamethyltriethylenetetraamine (hmtrien) has been studied at 298 K in the aprotic solvent dimethyl sulfoxide (DMSO) and in an ionic medium set to 0.1 mol.dm(-3) with Et4NClO4 under anaerobic conditions. UV/Vis spectrophotometric and calorimetric measurements have been carried out to obtain the thermodynamic parameters for the systems investigated. Mononuclear 1:1 complexes are formed for all systems. In addition, trien also forms the ML2 mononuclear complex and a polynuclear M2L3 species with M = Cd2+ and Coll, All the complexes are enthalpy stabilized, whereas the entropy changes counteract the complex formation. The results are discussed in terms of the different basicities, steric requirements and solvation both of the ligands and of the complexes formed. The influence of N-alkylation on the selectivity of the ligands towards metal ions is analysed. In the case of the Co-II complexes, their ability to take up dioxygen has also been studied by voltammetric and UV/Vis measurements and gasometric absorption. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.