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31P NMR and potentiometric titration experiments allowed the complete microconstant system to be resolved

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Stability in aqueous solution of some complexes of heavy metals with diaza‐polyoxamacrocyclic ligands Stability of metal complexes (Mn+ = Cu2+, Ni2+, Co2+, Zn2+, Pb2+, Ag+ and Cd2+) with five diaza‐polyoxamacrocycles (L = [2.1.1], [2.2.1], [2.2.2], [2.1] and [2.2] ) have been determined at 25°, in 0.1 M Et4N+ClO 4− aqueous solutions, by means of potentiometric titrations. All cations form MLn+ complexes; Cu2+ also forms the MHL(n+1)+ protonated species with both [2.2.1] and [2.1.1] ligands. The stability of these complexes has been discussed in terms of structure and by considering the ionic radii of the cations together with the radii of the macrocyclic cavities. Different behaviour is observed between some of these complexes and the well known alkali and alkaline‐earth cryptates, partly due to the more covalent nature of bonds formed by the investigated cations and the donor sites of the ligands. The effect of the substitution of two oxygen by two sulfur atoms in the pentadentate ligand [2.1] on the stability of the complexes is reported.