Résumé
The stability and the selectivity of 1:1 complexes formed by Ag+, Pb2+, Cu2+ cations with two of Schiff-Base bibracchial lariat ethers, derived from bis(p-formyl)-benzyl-4,13-diaza-18-crown-6 with aniline and anisidine, has been studied by UV-VIS spectrometry. The selectivity of these macrocyclic receptors in the complexation of Ag+, Pb2+ and Cu2+ cations, as analysed by spectrometric data is in good agreement with the selectivity determined by potentiometric methods and it follows the dimensional compatibility between the diameter of macrocyclic cavity and the diameter of metallic cation, accompanied by a coordination behaviour by the macrocyclic nitrogen atoms: the selectivity in complexation of Pb2+ and Ag+ cations, is higher than the selectivity in Cu2+ complexation. The results of spectrometric analyses have been confirmed by a potentiometric study that establishes the next succession of selectivity: S-A9(/Cu)+(2+) > S (+)(2+)(Ag)(/Pb) > S (2+)(2+)(Pb)(/Cu), available for both receptors.