An iterative extended Huckel molecular orbital calculation is used to obtain wave functions for the ground state of biferrocenylene [bis(fulvalene)diiron] and several low-lying states of the mono- and dioxidized cations. The molecular orbitals are compared to those calculated for biferrocene and to those obtained from a previous study of ferrocene and the ferrocenium ion. The calculated electron distributions are used to determine the electric field gradient at each iron nucleus for bis(fulvalene)diiron and biferrocene. A large quadrupole splitting, comparable to that calculated for ferrocene, is obtained for both compounds in agreement with experiment. The ground state of monooxidized bis(fulvalene)diiron is obtained by removal of an electron from an e2g type orbital delocalized over the two ferrocene moieties due to d-orbital relaxation effects similar to those observed for the ferrocenium ion. For the monovalent cation, the electric field gradient at the iron nuclei and g values are calculated. The values are in agreement with experiment. A possible assignment of the electronic spectral transitions unique to the mixed-valence state is made. Such d-orbital relaxation effects are not observed for the dioxidized species. The ground state of the divalent cation is obtained by removal of two electrons from the highest occupied molecular orbital of the neutral species, a delocalized carbon π orbital with substantial metal-metal antibonding character. The calculated diamagnetic ground state is the basis for a consistent explanation of the unexpectedly large quadrupole splitting and other observed spectroscopic properties. Removal of electrons from a1g or degenerate e2g type d orbitals yields excited configurations which do not account for the observed behavior of dioxidized bis(fulvalene)diiron. © 1976, American Chemical Society. All rights reserved.