  A combined high-resolution Fourier transform infrared (FTIR) spectra of
ferrocene (Fc) and density functional theory (DFT) based quantum mechanical
calculations confirmed the dominance of the eclipsed Fc conformer in the
fingerprint region of 400-500 cm-1. The IR spectra of Fc were measured in
solutions with a number of non-polar solvents such as acetonitrile,
dichloromethane, tetrahydrofuran and dioxane. The measurements agree well with
the earlier IR spectra of Lippincott and Nelson (1958) as well as the most
recent IR spectral measurement in dichloromethane solution of Duhovic and
Diaconescu (2013). All experimental measurements in the solutions unambiguously
exhibit an IR spectral splitting of ca. 15 cm-1 in the 480-500 cm-1 region. The
DFT based B3LYP/m6-31G(d) quantum mechanical calculations using implicit
solvent models in this study indicates that only the ground electronic state of
the eclipsed (D5h) Fc splits in the IR fingerprint region of ca. 500 cm-1. The
IR spectral splitting characterises the centre Fe metal related vibrations of
the eclipsed Fc, in agreement with our previous finding in gas phase [Mohammadi
et al, 2012]. The present study further suggests that the effects of solvents
on the IR spectra of Fc in this region are small and the solvent model effects
are also small but the solute molecular density (SMD) model seems to produce
the most accurate IR spectrum in the region of 400-600 cm-1 of Fc without
scaling the calculated results.
