Synthesis of an unsymmetrical N-functionalized triazacyclononane ligand and its Cu(II) complex

The unsymmetrical 1,4-bis(2-aminophenyl)-7-(pyridin-2-ylmethyl)-1,4,7-triazacyclononane ligand (L3) has been prepared and characterized by NMR spectroscopy. The L3 ligand is based on the triazamacrocycle ring bearing one flexible 2-pyridylmethyl linked to the macrocycle group via the methyl group, and two rigid 2-aminophenyl pendant donor groups linked to the macrocycle via the aromatic carbon atoms. Reaction of this ligand with Cu(ClO4)2·6H2O afforded the corresponding complex [Cu(L3)](ClO4)2·H2O (4) which was structurally characterized both in solid state and in solution. The crystal structure of 4 consists of a discrete monomeric [Cu(L3)]2+ in which the Cu(II) ion is six coordinated with three nitrogen atoms of the macrocycle ring, two of the aminophenyle and one of the pyridine appended functions. The triazacyclonane macrocycle ring is facially coordinated and the N-donor atoms of the three pendant groups (two aniline and one pyridine groups), are disposed in the same side of the basal macrocyclic ring, leading to a distorted and elongated CuN4N2 octahedron. UV–Vis spectroscopy of complex 4 in acetonitrile displays a d–d transition band at λ = 673 nm. The voltammetric studies show that the [Cu(L3)]2+ cation can be reduced quasi-reversibly and oxidized irreversibly, both process being monoelectronic.