Electronic structure and intrinsic redox properties of [2Fe-2S]+ clusters with tri- and tetracoordinate iron sites

Using potentially bidentate ligands (-SC2H4NH2), we produced 2Fe-2S]+ species of different coordination geometries by fission of 4Fe-4S]2+ complexes. Even though the ligands are monodentate in the cubane complexes, both mono- and bidentate complexes were observed in the 2Fe] fission products through self-assembly because of the high reactivity of the tricoordinate iron sites. The electronic structure of the 2Fe] species was probed using photoelectron spectroscopy and density functional calculations. It was found that tetracoordination significantly decreases the electron binding energies of the 2Fe] complexes, thus increasing the reducing capability of the 2Fe-2S]+ clusters.