PNNL

Abstract

The electronic structure of a series of Fe-S complexes, Fe(SCN)(3)(-), Fe(SCN)(4)(-), Na+[Fe(SCN)(4)(2-)], Fe(SCH3)(3)(-), Fe(SCH3)(4)(-), Na+[Fe(S-2-o-xyl)(2)(2-)], and Fe(S-2-o-xyl)(2)(-) (where S-2-o-xyl = o-xylene-alpha,alpha'- dithiolate), was investigated in the gas phase using photodetachment photoelectron spectroscopy. Spectral features due to detachment from metal d orbitals or ligand orbitals were distinguished by comparing with the spectrum of a d(0) complex, Sc(SCN)(4)(-). A weak threshold feature was observed in the spectra of all ferrous complexes due to detachment of the minority spin Fe 3d electron [Fe-II (3d(6)) --> Fe-III (3d(5))]. The spin majority Fe 3d electron signals were observed at much higher binding energies, revealing directly the "inverted level scheme" for these [1Fe] Fe-S complexes based on previous spin polarized calculations. The "inverted level scheme" is shown to be a general feature of the electronic structures of the [1Fe] Fe-S complexes, independent of the oxidation state and coordination number. Information about the gas-phase redox potentials and reorganization energies upon oxidation of the ferrous complexes is obtained from the adiabatic and vertical detachment energies of the minority Fe 3d electron.