OPTICAL AND MAGNETIC-PROPERTIES OF IRON(II) NITROSYL COMPLEXES IN MODEL COMPOUNDS

The iron(II) nitrosyl complexes [FeL(NO)] (L = ethylenediamine-, ethylenedioxydiethylenedinitrilo- or 1,6-diaminohexane-N,N,N',N'-tetraacetate) have been studied by absorption, low-temperature magnetic circular dichroism (MCD) and EPR spectroscopies. All three complexes exhibit similar spectral properties. The EPR spectra can be understood in terms of an axial site with a S = 3/2 electronic ground state. Analysis of the optical spectra has been carried out following extended-Huckel molecular orbital calculations on [Fe(H2O)5(NO)]2+ assuming C4v symmetry for the iron(II) ion with the Fe-NO bond providing the major axis of distortion. Thus it has been possible to identity and assign the MCD transitions within the Fe-NO fragment of the complexes. This analysis provides a basis for understanding and interpreting the magneto-optical spectra of the nitrosyl complexes of iron(II) sites in non-haem iron proteins.