Polyamine ligands. III. Five-coordinate complexes with the quinquedentate N,N,N'-Tris[2-(2'-pyridyl)ethylethylenediamine

Abstract

The quinquedentate ligand, N,N,N?-tris[2-(2?- pyridyl)ethyl]ethylenediamine (tpen), has been synthesized from ethylenediamine and 2-vinylpyridine. The free amine tpen is thermally unstable, but readily forms chemically stable metal complexes of the composition [M(tpen)](ClO₄)₂ (M = Cu, Ni, Zn) and [Co(tpen)O₂Co(tpen)]- (ClO₄)₄. In each of these compounds, the amine tpen is bonded to the metal ion through all five of its nitrogen atoms, as indicated by infrared and electronic absorption spectra and magnetic susceptibility measurements. The compound [Ni(tpen)](ClO₄)₂ shows four d-d transitions whose energies correspond closely to the values predicted from a ligand field calculation for a square pyramidal NiN₅ chromophore. This structure has been confirmed by X-ray diffraction analysis. These complexes of tpen are the first reported quinquedentate pentaamine chelate structures of copper(II), nickel(II), and zinc(II).