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

Abstract

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution III. The Monocycle [22]‐Py 2 N 4 The nature and stability of complexes formed by a new 22‐membered monocycle L = [22]‐Py 2 N 4 with the cations M n+ = Cu 2+ , Co 2+ , Ni 2+ , Zn 2+ , Cd 2+ , Pb 2+ , and Ag + have been determined in aqueous solutions (0.01M NaClO 4 , 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 ML n+ were identified in all systems investigated, but the dinuclear species M 2 L 2n+ were only found with Cu 2+ and Ag + . The logarithms of the overall stability constants for the copper and silver complexes are CuL 2+ , 12.9; Cu 2 L 4+ , 18.6; Agl + , 6.3; Ag 2 L 2+ , 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.