The electronic structure of the electron–reservoir complex CpFe(hexamethylbenzene) revisited: a regular metal-centered SOMO

While all the available experimental and theoretical data on 19-electron electron reservoir complexes of the general type (η5-C5R5)Fe(η6-arene) (R = H, Me) agree for a SOMO participation of Fe being larger than that of the Cp and arene ligands, recent DFT calculations disagree on only one compound, namely CpFe(HMB) (HMB = hexamethylbenzene). The reported calculations show clearly that CpFe(HMB) is not an exception and has iron-based SOMO, like all the members of the (η5-C5R5)Fe(η6-arene) (R = H, Me) family.