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

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.

Doumy, GillesArgonne National Laboratory (author)
Andersen, AmityPacific Northwest National Laboratory (author)
Al Haddad, AndreArgonne National Laboratory (author)
Kumagai, YoshiakiArgonne National Laboratory (author)
Tu, Ming FengNorthwestern University,Argonne National Laboratory (author)
Bang, JooheeArgonne National Laboratory (author)
Bostedt, ChristophArgonne National Laboratory,Northwestern University (author)
Uhlig, JensLund University,Lunds universitet,NanoLund: Centre for Nanoscience,Annan verksamhet, LTH,Lunds Tekniska Högskola,Kemisk fysik,Enheten för fysikalisk och teoretisk kemi,Kemiska institutionen,Institutioner vid LTH,Other operations, LTH,Faculty of Engineering, LTH,Chemical Physics,Physical and theoretical chemistry,Department of Chemistry,Departments at LTH,Faculty of Engineering, LTH(Swepub:lu)chem-jnu (author)
Nascimento, Daniel R.Pacific Northwest National Laboratory (author)
Assefa, Tadesse A.European XFEL GmbH (author)
Németh, ZoltánWigner Research Centre for Physics, Hungarian Academy of Sciences (author)
Vankó, GyörgyWigner Research Centre for Physics, Hungarian Academy of Sciences (author)
Gawelda, WojciechAdam Mickiewicz University in Poznań,European XFEL GmbH (author)
Govind, NiranjanPacific Northwest National Laboratory (author)
Young, LindaArgonne National Laboratory,University of Chicago (author)
Argonne National LaboratoryPacific Northwest National Laboratory (creator_code:org_t)

By the author/editor: March, Anne Mari ...; Doumy, Gilles; Andersen, Amity; Al Haddad, Andre; Kumagai, Yoshiak ...; Tu, Ming Feng; show more...; Bang, Joohee; Bostedt, Christo ...; Uhlig, Jens; Nascimento, Dani ...; Assefa, Tadesse ...; Németh, Zoltán; Vankó, György; Gawelda, Wojciec ...; Govind, Niranjan; Young, Linda; show less...

About the subject

NATURAL SCIENCES: NATURAL SCIENCES; and Chemical Science ...; and Physical Chemist ...

NATURAL SCIENCES: NATURAL SCIENCES; and Physical Science ...; and Atom and Molecul ...

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