Vibrational Spectroscopy and Computational Studies of Polyhalogenated Ferrocenes

In this work we have provided the first comprehensive investigation of the vibrational spectra of polyhalogenated haloferrocenes; viz 1,1′-dibromoferrocene, 1,1′,2,2′-tetrabromoferrocene, 1,1′,2,2′,3,3′-hexabromoferrocene and 1,1′,2,2′-tetraiodoferrocene. These are characterised by infrared, Raman and inelastic neutron scattering (INS) spectroscopies supported by periodic density functional theory calculations of the primitive cell. The spectra differ from those of ferrocene in the region below 500 cm−1 because the C–Br and C–I modes occur here. The modes in this region include the frustrated rotational and translational modes of the iron atom and the Cp rings. Some of these are present as whole-molecule librations and translations below 100 cm−1 but some become intramolecular modes of the entire molecule—ring tilts and bends—and these are mass-dependent.