Synthesis and Characterization of Copper, Nickel and Cobalt Complexes of N,N′‐Dimethyl‐2,11‐diaza[3,3](2,6)pyridinophane

The properties of the tetraazamacrocyclic compound N,N′‐dimethyl‐2,11‐diaza[3,3](2,6)pyridinophane (L‐N4Me2) as a ligand for some selected metal chlorides have been examined. The crystal structure of the uncoordinated ligand reveals a syn chair‐chair conformation. In solution, the ligand displays fluctional behavior. Reaction of L‐N4Me2 with the chlorides of copper(II), nickel(II), and cobalt(II) affords the complexes [Cu(L‐N4Me2)Cl2] · H2O (3), [Ni(L‐N4Me2)(H2O)Cl]Cl · H2O (4), and [Co(L‐N4Me2)Cl2] · 2 H2O (5) in which the ligand adopts a syn boat‐boat conformation. The crystal structures of 4 and 5 are presented. Due to the small cavity of the 12‐membered ring of the ligand, exclusively distorted cis‐octahedral coordination geometries are found at the metal sites. A comparison of structural data of several complexes with this ligand shows that the extent of the distortions from ideal octahedral geometry is mainly determined by the M‐Npy bond strength. The electronic as well as the solution properties of the described complexes have been investigated by electronic absorption spectroscopy. ESR spectroscopy, and electrochemical methods.