Affinity of lanthanide(III) ions for oxygen- and mixed oxygen-nitrogen-donor ligands in dimethylsulfoxide: a thermodynamic and spectroscopic investigation

The interactions of lanthanide(III) ions with the following oxygen- and mixed oxygen-nitrogen-donor ligands: 2-methoxyethylamine (L1), 2-aminoethanol (L2), 2-methoxyethylether (L3), di(ethyleneglycol) (L4), 2,2'-oxydiethylamine (L5) and 1,5-diaminopentane (L6) have been investigated in dimethylsulfoxide (DMSO) at 298 K and I=0.1 mol dm(-3) (Et4NClO4)Calorimetric and H-1 NMR results show that L1-L4 and L6 are not able to complex Ln(III) ions. L5 is shown to be able to bind heavier Ln(III) ions (Ln=Ho-Lu). Potentiometric and calorimetric measurements have been carried out to obtain the Ln(III)-L5 thermodynamic parameters of complexation. All the complexes are formed in exothermic reactions being the entropy terms generally negative or slightly positive. Comparison between the complexing abilities of L1 and L5 shows that at least two - CH2CH2NH2 side-arms added to an ether function are needed to promote effective interaction between an ether O atom and Ln(III) ions in the high coordinating solvent DMSO. The results are discussed in terms of different donor properties and solvation of -NR- and -O- groups towards metal ions. A comparison with data previously obtained in DMSO for the complex formation of Ln(III) with the purely N donor diethylenetriamine (dien) is made.