Aromaticity and ring currents in ferrocene and two isomeric sandwich complexes

Ring currents induced in the ferrocene molecule and its two hypothetical isomers (η4-C4H4)Fe(η6-C6H6) and (η3-C3H3)Fe(η7-C7H7) by an external magnetic field directed along the principal axis are plotted within the ipsocentric approach (at the B3LYP/6-31G∗∗//B3LYP/6-31G∗∗ level). The carbocyclic ligands in all three species are found to be aromatic, i.e. to support individual diatropic ring currents, with formal charges that are consistent with the 4n + 2 rule and the +2 oxidation state of iron.