title: Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene.
abstract: Molecular distortion of dynamic molecules gives a clear signature in the vibrational spectra, which can be modeled to give estimates of the energy barrier and the sensitivity of the frequencies of the vibrational modes to the reaction coordinate. The reaction coordinate method (RCM) utilizes ab initio-calculated spectra of the molecule in its ground and transition states together with their relative energies to predict the temperature dependence of the vibrational spectra. DFT-calculated spectra of the eclipsed (D5h) and staggered (D5d) forms of ferrocene (Fc), and its deuterated analogue, within RCM explain the IR spectra of Fc in gas (350 K), solution (300 K), solid solution (7-300 K), and solid (7-300 K) states. In each case the D5hrotamer is lowest in energy but with the barrier to interconversion between rotamers higher for solution-phase samples (ca. 6 kJ mol-1) than for the gas-phase species (1-3 kJ mol-1). The generality of the approach is demonstrated with application to tricarbonyl(η4-norbornadiene)iron(0), Fe(NBD)(CO)3. The temperature-dependent coalescence of the ν(CO) bands of Fe(NBD)(CO)3is well explained by the RCM without recourse to NMR-like rapid exchange. The RCM establishes a clear link between the calculated ground and transition states of dynamic molecules and the temperature-dependence of their vibrational spectra.
authors.affiliation: School of Chemistry, University of Melbourne, Parkville, Victoria, 3010, Australia.
authors.forename: Stephen P
authors.identifier: http://orcid.org/0000-0002-9399-3560
authors.initials: SP
authors.lastname: Best
authors.affiliation: Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn, Melbourne, Victoria, 3122, Australia.
authors.forename: Feng
authors.identifier: http://orcid.org/0000-0002-6584-0516
authors.initials: F
authors.lastname: Wang
authors.affiliation: School of Chemistry, University of Melbourne, Parkville, Victoria, 3010, Australia.|School of Physics, University of Melbourne, Parkville, Victoria, 3010, Australia.
authors.forename: M Tauhidul
authors.initials: MT
authors.lastname: Islam
authors.affiliation: Department of Chemistry and Biotechnology, Swinburne University of Technology, Hawthorn, Melbourne, Victoria, 3122, Australia.
authors.forename: Shawkat
authors.initials: S
authors.lastname: Islam
authors.affiliation: Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria, 3168, Australia.
authors.forename: Dominique
authors.initials: D
authors.lastname: Appadoo
authors.affiliation: School of Physics, University of Melbourne, Parkville, Victoria, 3010, Australia.
authors.forename: Ryan M
authors.initials: RM
authors.lastname: Trevorah
authors.affiliation: School of Physics, University of Melbourne, Parkville, Victoria, 3010, Australia.
authors.forename: Christopher T
authors.identifier: http://orcid.org/0000-0001-6608-0048
authors.initials: CT
authors.lastname: Chantler
keywords: IR spectroscopy; ab initio calculations; ferrocene; fluxionality; molecular dynamics; vibrational spectroscopy