Metal complexes of N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN): Variable coordination numbers and geometries

We report X-ray crystal structures of complexes of the membrane-permeable metal chelator N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) with Cu(II) and Zn(II), and solution studies of the Zn(II) and Cd(II) complexes. [Zn(II)(TPEN)](PF6)2 exhibits a distorted octahedral geometry with hexadentate TPEN, whilst [Cu(II)(TPEN)](PF6)2 contains penta-coordinated Cu(II), with one pendant picolyl arm of TPEN. A survey of structures of metal–TPEN complexes reveals the versatility of the TPEN ligand. Complexes of V(V), Cr(III), Rh(III), Re(VII), Fe(II), as well as Cu(II) are known which contain hypodentate TPEN with 3–5 of its nitrogens coordinated to the metal. Solution NMR spectroscopic studies also suggest that there is dynamic conformational flexibility in the structures of the [Zn(TPEN)]2+ and [Cd(TPEN)]2+ complexes in aqueous solution.

Interesting variations in the structures of Cu(II), Zn(II) and other metal complexes of N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) are described.Figure optionsDownload as PowerPoint slide