IR spectra of products of the reactions of methyl halogen
molecules CH3Cl and CH3Br with Mg
have been
studied under matrix isolation conditions. Comparison of the
spectra with ab initio frequencies and intensities
allows us to identify the primary reaction products as monomagnesium
Grignard complexes CH3MgX (X =
Cl, Br) and therefore reject the possibility of creation of
energetically more stable bimagnesium species
CH3MgMgX. Those species according to ab initio calculations should be
bound with respect to the decomposition
CH3MgX + Mg. Ab initio calculations have been
carried out at several levels, including the large basis
set
MP2 and DFT treatments. The scaling factors, which bring the
computed harmonic frequencies into
correspondence with the experimental band positions, have been deduced.
It is shown that, unlike the majority
of organic molecules, organometallic complexes should be considered
more carefully, in the sense that the
scaling factors of the advanced MP2 and DFT procedures are not as close
to unity as is believed.
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