Thermodynamics of complexation of cadmium(II) by open-chain N-donor ligands in dimethyl sulfoxide solution

Thermodynamic parameters for the complexation of Cd-II by the amines n-butylamine (n-but), ethylenediamine (en), N,N'-dimethylethylenediamine (dmen), N,N,N'-trimethylethylenediamine (trmen), N,N,N',N'-tetramethylethylenediamine (tmen), diethylenetriamine (dien), N,N"-dimethyldiethylenetriamine (dmdien), and N,N,N',N",N"-pentamethyldiethylenetriamine (pmdien) have been determined in dimethyl sulfoxide (DMSO) solution by potentiometric and calorimetric techniques at 298 K and 0.1 mol dm(-3) ionic strength (NEt4ClO4). Only mononuclear complexes are formed, in which the polyamines act predominantly as chelating agents. All the complexes are enthalpy-stabilized, whereas the entropy changes counteract the complexation. The steric requirements of the donors have a strong influence on the stoichiometry and nature of the Cd-II complexes formed. Comparisons are made with data reported for some of these systems in water and with available data on silver(I) complexation by the same amines in DMSO, the latter showing that the selectivity of the ligands towards metal ions is also influenced by N-alkylation.