Aromaticity and ring currents in ferrocene and two isomeric sandwich complexes

Abstract Ring currents induced in the ferrocene molecule and its two hypothetical isomers (η 4 -C 4 H 4 )Fe(η 6 -C 6 H 6 ) and (η 3 -C 3 H 3 )Fe(η 7 -C 7 H 7 ) 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 4 n  + 2 rule and the +2 oxidation state of iron.