Vibrational spectra of ferrocene, ferrocene-containing polymers and their oxidized compounds

Ferrocene-containing polymers are an important member in the class of redox- responsive polymers, changing e.g. their solubility or conformation upon external stimuli. We present a study of their vibrational spectra using inelastic neutron scattering, focusing on the central building block of these polymers, the organometallic ferrocene complex. The vibrational modes of a bulk ferrocene sample are compared to those of poly(vinylferrocene), poly(ferrocenyldimethylsilane) and poly(ferrocenylmethylsilane). In the former polymer, the ferrocene complex is laterally attached to the polymer chain and the vibrational spectrum shows a slight shift and broadening of the fingerprint modes in the range of 100-800 cm⁻¹ except for the ring-metal-ring stretching mode which was not detectable anymore. The latter two polymers, where the ferrocene complex is part of the polymer backbone, exhibit larger differences to the vibrational spectrum of bulk ferrocene. Moreover, several contributions to the spectra caused by methyl groups in these polymers could be identified. In order to study the influence of oxidation on ferrocene and redox-responsive polymers, we investigated the ionic compound ferrocenium triiodide and oxidized poly(vinylferrocene). It is observed that the weakening of the η⁵-complex bond by a missing electron leads to a significant shift of the fingerprint modes to lower frequencies.