Theoretical investigation of the structure and nature of the interaction in metal-alkane σ-complexes of the type [M(CO)5(C2H6)] (M = Cr, Mo, and W)

Density Functional Theory calculations were carried out to study the structure, energetics of the interactions and nature of the bonds in the metal-alkane σ-complexes of the type M(CO)5(C2H6) M = Cr, Mo, and W. Only the η1 coordination mode through hydrogen is obtained. The vibrational frequencies showed that upon coordination the ν(C-H)asym mode has an important red shift of 273 cm−1 and thus may be an important mode to characterize and follow the alkane coordination to the metallic fragment. TD-DFT calculations of the electronic transitions show that the coordination of the alkane affects drastically the metal to ligand charge transfer (MLCT) band of the metallic fragment, showing a blue shift of 163 nm. The computed AIM local properties (ρ(r), ∇2(ρ), G(r), V(r) and H(r)) in conjunction with the Morokuma energy decomposition analysis (EDA) and also comparisons with the water dimer, suggest that this metal-alkane interaction may also be viewed as an unconventional hydrogen bond, with significant charge transfer and polarization contribution.