Elucidation of the photoaquation reaction mechanism in ferrous hexacyanide using synchrotron x-rays with sub-pulse-duration sensitivity

Research output: Contribution to journalArticle


Ligand substitution reactions are common in solvated transition metal complexes, and harnessing them through initiation with light promises interesting practical applications, driving interest in new means of probing their mechanisms. Using a combination of time-resolved x-ray absorption spectroscopy and hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics simulations and x-ray absorption near-edge spectroscopy calculations, we elucidate the mechanism of photoaquation in the model system iron(ii) hexacyanide, where UV excitation results in the exchange of a CN- ligand with a water molecule from the solvent. We take advantage of the high flux and stability of synchrotron x-rays to capture high precision x-ray absorption spectra that allow us to overcome the usual limitation of the relatively long x-ray pulses and extract the spectrum of the short-lived intermediate pentacoordinated species. Additionally, we determine its lifetime to be 19 (±5) ps. The QM/MM simulations support our experimental findings and explain the ∼20 ps time scale for aquation as involving interconversion between the square pyramidal (SP) and trigonal bipyramidal pentacoordinated geometries, with aquation being only active in the SP configuration.


  • Anne Marie March
  • Gilles Doumy
  • Amity Andersen
  • Andre Al Haddad
  • Yoshiaki Kumagai
  • Ming Feng Tu
  • Joohee Bang
  • Christoph Bostedt
  • Jens Uhlig
  • Daniel R. Nascimento
  • Tadesse A. Assefa
  • Zoltán Németh
  • György Vankó
  • Wojciech Gawelda
  • Niranjan Govind
  • Linda Young
External organisations
  • Argonne National Laboratory
  • Pacific Northwest National Laboratory
  • Northwestern University
  • European XFEL GmbH
  • Wigner Research Centre for Physics, Hungarian Academy of Sciences
  • Adam Mickiewicz University in Poznań
  • University of Chicago
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Chemistry
Original languageEnglish
Article number144306
JournalJournal of Chemical Physics
Issue number14
Publication statusPublished - 2019
Publication categoryResearch