A new multivalent cluster: synthesis, electrochemistry, solid state structure and computational studies on the iron-nickel mixed-metal nitride anions [Fe(6)Ni(6)N(2)(CO)(24)](n-) (n=2-4)

The three clusters [Fe(6)Ni(6)N(2)(CO)(24)](n-) (n = 2-4) have been isolated, and their solid-state structures determined. The clusters are composed by three face-sharing octahedra, with the external ones filled by two interstitial nitride. The addition of electrons brings about swelling of the central, empty octahedron. Cyclic voltammetry shows that redox conversions of the three clusters are totally reversible. Extended Huckel and density functional calculations have been performed, to explain this behavior