In this paper, metallocene-fullerene hybrid complexes, [M(η5-Cp)(η5-C60Me5)] (M = Fe2+, Ru2+, Os2+), as well as corresponding classical metallocenes have been studied theoretically at BP86/def2-SVP and M06L/def2-SVP levels of theory. With considering these metal complexes as an ABA′ system (B is the central metal ion and A and A′ are related η5-ligands), the total interaction energies were calculated using common methods, as well as by calculating the interaction energies between the four defined pairs of fragments including A–B, B–A′, A–BA′, and AB–A′. The resulting data clearly showed that in all complexes there is a strong anticoopertivity between two metal-(η5-ligand) bonds. In order to understand the origin of difference in values of various calculated interactions in above two types of complexes, the nature of metal–ligand bonds was also studied using energy decomposition analysis-natural orbital for chemical valence calculations. The results showed that in hybrid complexes, in contrast to metallocenes, the orbital interactions are considerably larger than electrostatic interactions.
