Theoretical study of bonding, structure, and vibrational spectra of the [Fe2(CO)8]2- anion and its derivatives

A theoretical study of the structural versatility of the di-iron carbonylate, [Fe-2(CO)(8)](2-) and of its adducts with electrophiles is presented. The geometries of three energy minima and four transition states of [Fe-2(CO)(8)](2-) have been characterized, and the relative energies of several alternative structures have been evaluated. The calculated vibrational spectra in the Fe-Fe and the C=O stretching regions are discussed for the three isomers, and a good correlation between the Fe-Fe stretching force constant and the Fe-Fe bond distance is found for both theoretical and experimental data. The effect of the orientation of the terminal ligands on the Fe-Fe bond and the rearrangement of such ligands by the formation of adducts with electrophiles are also addressed.