An electron spin resonance study of the reaction of sulphide and dithionite with some iron(I) and iron(II) complexes: the valency and stereochemistry of iron in reduced non-haem iron proteins

Abstract

E.s.r. spectra have been recorded for [Fe(NO)(H₂O)₅]²⁺ in sodium sulphide and sodium hydroxide solutions, and for [Fe(CN)₅NO]^2– reduced by sodium dithionite and sodium sulphide. In each case, formulae or structures are suggested for the species responsible for the signals. Analysis of the published e.s.r. spectra from reduced non-haem iron Proteins shows that all valencies of iron other than +1 and all co-ordination numbers other than 6 are incompatible with the existing spectra, and that two g-values significantly lower than 2 can only be accommodated if vacant low-lying π* ligand orbitals are present. The e.s.r. spectra of reduced [Fe(NO₂)(CN)₅]^4– is very similar to that of reduced non-haem iron proteins, and so it could be treated as a model for the natural compound.