Theoretical investigation of the structure and nature of the interaction in metal–alkane σ-complexes of the type [M(CO) 5(C 2H 6)] (M = Cr, Mo, and W)

Abstract

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(C 2H 6) M = Cr, Mo, and W. Only the η 1 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.