Nature et stabilité des complexes métalliques de cryptands dinucléants en solution. I. Polyazapolyoxa macrotricycle cylindrique et monocycle constitutif

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution. I. A Polyazapolyoxa Cylindrical Macrotricycle and its Monocyclic Subunit pH‐metry and UV spectrophotometry were used to study the complexing properties of the cylindrical macrotricycle, 1,7,13,19‐tetraaza‐4,16‐dioxa‐10,22,27,32‐tetraoxatricyclo[17.5.5.5]tetratriacontane ( 1 ) and of its constitutive monocyclic subunit, 1,7‐diaza‐4,10‐dioxacyclododecane ( 2 ) with some transition and heavy metal cations (Cu 2+ , Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Pb 2+ , Ag + ), in aqueous medium 0.1M Et 4 NClO 4 , at 25°. The protonation constants of the ligands as well as the nature and the stabilities of the complexes formed in the pH‐regions studied were determined. The tricycle 1 only formed dinuclear M 2 L complexes with Cu 2+ , Zn 2+ , and Ag + , accompanied in the latter case by a protonated mononuclear MLH species, and with Cu 2+ and Zn 2+ at high pH‐values by dinuclear hydroxo complexes. Only mononuclear complexes were evidenced with the other cations, ML being accompanied either by protonated or hydroxy mononuclear species. The mononuclear complexes of 1 , when they existed, were more stable than the corresponding complexes of 2 , except for cobalt which formed complexes of comparable stability with both ligands. In the other cases (Cd 2+ , Pb 2+ , Ag + ), the stability differences between the complexes of 1 and 2 increased with the size of the cation.