Nature et stabilité des complexes métalliques de cryptands dinucléants en solution. III. Le monocycle [22]-Py2N4

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution III. The Monocycle 22]-Py₂N₄ The nature and stability of complexes formed by a new 22-membered monocycle L = 22]-Py₂N₄ with the cations Mⁿ⁺ = Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Ag⁺ have been determined in aqueous solutions (0.01M NaClO₄, 25°) by pH-metry and also, for the copper system, by UV-absorption spectrophotometry. The stepwise protonation constants of the four amine functions of L were 9.1, 8.3, 7.1 and 3.7 logarithms units, respectively. No evidence was found for the protonation of the two pyridine nitrogen atoms. Mononuclear complexes MLⁿ⁺ were identified in all systems investigated, but the dinuclear species M₂L²ⁿ⁺ were only found with Cu²⁺ and Ag⁺. The logarithms of the overall stability constants for the copper and silver complexes are CuL²⁺, 12.9; Cu₂L⁴⁺, 18.6; Agl⁺, 6.3; Ag₂L²⁺, 10.9, respectively. Mononuclear hydroxy species MLOH^(n?1)+ were identified in all systems except those of copper and silver. No dinuclear hydroxy complexes were detected. The complexing properties of L are compared to those of the large and less rigid bis-dien.