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

摘要

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-hexaemethyltriethylenetetraamine (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 Et_4NClO_4 under anaerobic conditions. UV/Vis spectrophotometric and caorimetric 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 ML_2 mononuclear complex and a polynuclear M_3L_3 species with M=Cd~(2+) and Co~(2+). 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.