Resolution of ferrocene and deuterated ferrocene conformations using dynamic vibrational spectroscopy: experiment and theory

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dc.contributor.authorTrevorah, RMen_AU
dc.contributor.authorTran, NTTen_AU
dc.contributor.authorAppadoo, DRTen_AU
dc.contributor.authorWang, Fen_AU
dc.contributor.authorChantler, CTen_AU
dc.date.accessioned2025-10-24T03:55:08Zen_AU
dc.date.available2025-10-24T03:55:08Zen_AU
dc.date.issued2020-06-01en_AU
dc.date.statistics2025-10-24en_AU
dc.description.abstractThe signature of molecular vibrations and distortions in dynamic molecules gives a complex fingerprint which is insightful and can substantiate (or otherwise) chemical hypotheses regarding molecular and conformer stability. Using high-accuracy experimental data of ferrocene (Fc) and deuterated ferrocene (dFc, Fc − d10) at temperatures from 7 K through to 388 K, we obtain complex spectral profiles which require an advanced reaction coordinate model to explain. We obtain compelling evidence that the single conformer model (staggered D5d or eclipsed D5h) used to interpret and explain many experimental results on ferrocene is invalid. However we also present compelling evidence that mixed conformer models are invalid, where ferrocene is represented by an effective dihedral angle between the cyclopentadienyl (Cp) rings; or by a mixture of Boltzmann populations of the two conformers. We find no evidence for single or mixed conformer models despite covering almost all conclusions from past literature for gas, solution or solid phase Fc. Some molecular dynamics computations have imputed free rotation at liquid helium temperatures or at room temperature – we find no evidence for either of these hypotheses. We measure and derive point-wise experimental uncertainty of the spectra, enabling quantitative assessment of specific chemical and physical models about the origin of the spectral line-shapes. A new principle based on the reaction coordinate is introduced. Advanced spectroscopy and modelling is introduced for hypothesis testing, to articulate the nature of the potential surface, the reaction coordinate and subtle conformational changes in dilute systems. Two expected spectral peaks appear inverted in the gas phase, but are explained by our Reaction Coordinate Method (RCM) model. The non-uniform broadening of the singlet and doublet peaks with increasing temperature is explained. Our experimental analysis shows that the lowest energy conformer is D5h for both Fc and dFc. We are able to represent the reduced mass ratios of the lowest vibrational modes for Fc and dFc of 1.11 for ν1 for Fc to Fc-d9 and of 1.10 for Fc to Fc-d10. The measured barrier height for rotation is 7.4 kJ mol−1 and 6.3 kJ mol−1 for Fc and dFc respectively, in comparison to numerous theoretical treatments and past experimental studies. For the first time, we obtain agreement of the model with the complex spectral evolution of profiles. These new techniques are sensitive discriminants of alternate models and chemical systems, which argues for wider application to other complex or impenetrable problems across fields arising for numerous other solutions, frozen or at room temperature. Crown Copyright © 2020 Published by Elsevier B.Ven_AU
dc.description.sponsorshipThis research was undertaken on the THz/Far-IR beamline at the Australian Synchrotron, Victoria, Australia. We acknowledge the Australian Research Council (ARC) and the science faculty of the University of Melbourne for funding this work. This research is supported by the AINSE Honours Scholarship Program. We acknowledge M. T. Islam, S. Islam and S. P. Best for their experimental and conceptual contributions to this work. In particular, this work and development would not have been possible without the experimental drive and insight of S. P. Best.en_AU
dc.identifier.articlenumber119491en_AU
dc.identifier.citationTrevorah, R. M., Tran, N. T. T., Appadoo, D. R. T., Wang, F., & Chantler, C. T. (2020). Resolution of ferrocene and deuterated ferrocene conformations using dynamic vibrational spectroscopy: experiment and theory. Inorganica Chimica Acta, 506, 119491. doi:10.1016/j.ica.2020.119491en_AU
dc.identifier.issn0020-1693en_AU
dc.identifier.journaltitleInorganica Chimica Actaen_AU
dc.identifier.urihttps://doi.org/10.1016/j.ica.2020.119491en_AU
dc.identifier.urihttps://apo.ansto.gov.au/handle/10238/16646en_AU
dc.identifier.volume506en_AU
dc.languageEnglishen_AU
dc.language.isoenen_AU
dc.publisherElsevieren_AU
dc.subjectInfrared spectraen_AU
dc.subjectFerroceneen_AU
dc.subjectOrganometallic compoundsen_AU
dc.subjectBondingen_AU
dc.subjectSymmetryen_AU
dc.subjectCatalysisen_AU
dc.subjectFuel Additivesen_AU
dc.subjectCrystalsen_AU
dc.subjectSolventsen_AU
dc.titleResolution of ferrocene and deuterated ferrocene conformations using dynamic vibrational spectroscopy: experiment and theoryen_AU
dc.typeJournal Articleen_AU
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