Theoretical Investigations on How to Reproduce d–π Bonds: Transition-Metal Cation–Benzene Complex Calculations

Abstract

Abstract Reproducibilities of d–π bonds were investigated on calculating complexes of first-row transition-metal cation (M+) and benzene (Bz). Calculations were carried out for half-sandwich MBz+ and sandwich MBz2+ complexes with several types of density functional theories (DFTs) and single-configurational wave function theories (WFTs). As a result, it was concluded that electron correlations are required to give the binding energies of d–π bonds even qualitatively, and DFTs would reproduce d–π bonds with quantitative accuracies only if electron correlations and long-range exchange interactions were both taken into consideration in exchange-correlation functionals used. In MBz+ calculations, WFTs fairly underestimated the binding energies for early transition metals (M = Sc–Cr) because of multiconfigurational effects. In contrast, DFTs overestimated them for late transition metals (M = Fe–Cu) due to insufficient long-range interactions in exchange functionals. For MBz2+, DFTs and WFTs gave similar binding energies for MBz2+, although WFTs slightly overestimated them for late transition metals. Furthermore, it was suggested that the experimental binding energies of CrBz2+ and MnBz2+ are probably misestimated.