Solid and solution state structures of mono- and di-nuclear iron(III) complexes of related hexadentate and pentadentate aminopyridyl ligands

Abstract

Two mononuclear iron(III) complexes formed with the related ligands N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (tpen) and N-benzyl-N,N′,N′-tris(2-pyridylmethyl)ethylenediamine (bztpen) have been studied. X-Ray crystallography reveals for the complex [Fe(tpen)][ClO₄]₃ that tpen acts as a hexadentate ligand in the solid state. In methanol or water containing solutions it was shown by EPR and UV-Vis spectroscopy that one pyridyl arm is exchanged by a solvent molecule. In dmf solution only partial exchange of a pyridyl arm was observed. The complex with the related pentadentate ligand bztpen [Fe(bztpen)Cl][ClO₄]₂ showed exchange of the coordinated chloride with methanol and water, but not with dmf. In water containing solutions both complexes are slowly converted into the dimeric μ-oxo complexes [(tpen)Fe^III(Cl)OFe^III(Cl)(tpen)]²⁺ or [(bztpen)Fe^III(Cl)OFe^III(Cl)(bztpen)]²⁺. This reaction is accelerated by addition of an excess of chloride.