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Redox pairs

The ETD option of the Bruker instrument allows us to study transition metal ligand complexes in different redox states. We can generate and isolate M2+-ligand complexes, which can then be charge-reduced via electron transfer from the anionic ETD-reagent forming the corresponding M1+-ligand complex. Either the 1+ or the 2+ complex can be isolated in the ion trap and IR spectra can be recorded for each of the redox pairs. Comparison with computed spectra can then be used to identify for instance changes in the ligand coordination upon reduction. We have studied complexes involving  nickel and copper in their II and I oxidation states with cyclen and crown ethers as host molecules, as well as of Ru(bpy)3 complexes (bpy is 2,2’-bipyridine). Ru(bpy)3 is among others used as dye-sensitizer in photovoltaic applications and has been the subject of extensive study.


  1. Vibrational spectra of the Ruthenium-tris-bipyridine dication and its reduced form in vacuo, Musleh U. Munshi
    Jonathan Martens, Giel Berden and Jos Oomens
    J. Phys. Chem. A 2020, 124, 2249-2459 (pdf file Open Access free download)

  2. Gas-Phase Infrared Ion Spectroscopy Characterization of Cu(II/I)Cyclam and Cu(II/I)2,2- Bipyridine Redox Pairs
    Musleh U. MunshiJonathan Martens, Giel Berden and Jos Oomens
    J. Phys. Chem. A 2019, 123, 4149-4157 (pdf file Open Access free download)

  3. Preparation of labile Ni+(cyclam) cations in the gas phase using electron-transfer reduction through ion–ion recombination in an ion trap and structural characterization with vibrational spectroscopy
    Musleh U. Munshi, Stephanie M. Craig, Giel Berden, Jonathan Martens, Andrew F. DeBlase, David J. Foreman, Scott A. McLuckey, Joss Oomens and Mark A. Johnson
    J. Phys. Chem. Lett. 2017, 8, 5047-5052 (pdf file Open Access free download)

Other studies on charge reduced systems using ETD:

  1. Radical‐Pairing Interactions in a Molecular Switch Evidenced by Ion Mobility Spectrometry and Infrared Ion Spectroscopy
    E. Hanozin, B. Mignolet, J. Martens, G. Berden, D. Sluysmans, A. Duwez, James F. Stoddart, G. Eppe, J. Oomens, E. De Pauw, D. Morsa
    Angewandte Chemie (2021), in press. (pdf file Open Access, free download).

  2. Structural identification of electron transfer dissociation products in mass spectrometry using infrared ion spectroscopy.
    J. Martens, J. Grzetic, G. Berden, and J. Oomens
    Nature Communications 7 (2016) 11754. (pdf file Open Access free download)

  3. Structures of Fluoranthene Reagent Anions Used in Electron Transfer Dissociation and Proton Transfer Reaction Tandem Mass Spectrometry.
    J. Martens, G. Berden, and J. Oomens
    Analytical Chemistry 88 (2016) 6126–6129. (pdf file Open Access free download)