Ligand substitution reactions are common in solvated transition metal complexes, and harnessing them through initiation with light promises interesting practical applications, driving an interest in new means of probing their mechanisms. In this work, using a combination of timeresolved x-ray absorption spectroscopy (XAS) and hybrid quantum mechanical, molecular mechanics (QM/MM) molecular dynamics (MD) simulations and x-ray absorption nearedge spectroscopy (XANES) 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 and kinetic fits suggest a formation time of 1.5 (0.6) ps. The QM/MM simulations support our experimental findings and explain the ~20 ps timescale for aquation as involving interconversion between the square pyramidal (SP) and trigonal bipyramidal (TBP) pentacoordinated geometries, with aquation being only active in the SP configuration.
March, Anne Marie, et al. "Elucidation of the photoaquation reaction mechanism in ferrous hexacyanide using synchrotron x-rays with sub-pulse-duration sensitivity." Journal of Chemical Physics, vol. 151, no. 14, Oct. 2019. https://doi.org/10.1063/1.5117318
March, Anne Marie, Doumy, Gilles, Andersen, Amity, Al Haddad, Andre, Kumagai, Yoshiaki, Tu, Ming-Feng, Bang, Joohee, Tu, Ming-Feng, Uhlig, Jens, Nascimento, Daniel R., Assefa, Tadesse A., Németh, Zoltán, Vankó, György, Gawelda, Wojciech, Govind, Niranjan, & Young, Linda (2019). Elucidation of the photoaquation reaction mechanism in ferrous hexacyanide using synchrotron x-rays with sub-pulse-duration sensitivity. Journal of Chemical Physics, 151(14). https://doi.org/10.1063/1.5117318
March, Anne Marie, Doumy, Gilles, Andersen, Amity, et al., "Elucidation of the photoaquation reaction mechanism in ferrous hexacyanide using synchrotron x-rays with sub-pulse-duration sensitivity," Journal of Chemical Physics 151, no. 14 (2019), https://doi.org/10.1063/1.5117318
@article{osti_1607390,
author = {March, Anne Marie and Doumy, Gilles and Andersen, Amity and Al Haddad, Andre and Kumagai, Yoshiaki and Tu, Ming-Feng and Bang, Joohee and Tu, Ming-Feng and Uhlig, Jens and Nascimento, Daniel R. and others},
title = {Elucidation of the photoaquation reaction mechanism in ferrous hexacyanide using synchrotron x-rays with sub-pulse-duration sensitivity},
annote = {Ligand substitution reactions are common in solvated transition metal complexes, and harnessing them through initiation with light promises interesting practical applications, driving an interest in new means of probing their mechanisms. In this work, using a combination of timeresolved x-ray absorption spectroscopy (XAS) and hybrid quantum mechanical, molecular mechanics (QM/MM) molecular dynamics (MD) simulations and x-ray absorption nearedge spectroscopy (XANES) 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 and kinetic fits suggest a formation time of 1.5 (0.6) ps. The QM/MM simulations support our experimental findings and explain the ~20 ps timescale for aquation as involving interconversion between the square pyramidal (SP) and trigonal bipyramidal (TBP) pentacoordinated geometries, with aquation being only active in the SP configuration.},
doi = {10.1063/1.5117318},
url = {https://www.osti.gov/biblio/1607390},
journal = {Journal of Chemical Physics},
issn = {ISSN 0021-9606},
number = {14},
volume = {151},
place = {United States},
publisher = {American Institute of Physics (AIP)},
year = {2019},
month = {10}}
Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division; USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Grant/Contract Number:
AC02-06CH11357
OSTI ID:
1607390
Alternate ID(s):
OSTI ID: 1608558 OSTI ID: 1570031
Journal Information:
Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 14 Vol. 151; ISSN 0021-9606
PROCEEDINGS OF THE 12TH INTERNATIONAL CONFERENCE ON SYNCHROTRON RADIATION INSTRUMENTATION – SRI2015, AIP Conference Proceedingshttps://doi.org/10.1063/1.4952871
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol. 377, Issue 2145https://doi.org/10.1098/rsta.2017.0464