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Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution
Stockholm University, Faculty of Science, Department of Physics.
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Number of Authors: 21
2015 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 520, no 7545, 78-81 p.Article in journal (Refereed) Published
Abstract [en]

Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site that need to be controlled to optimize complexes for photocatalytic hydrogen production and selective carbon-hydrogen bond activation. An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)5 insolution, that the photoinduced removal of CO generates the 16-electron Fe(CO)4 species, a homogeneous catalyst with an electron deficiency at the Fe centre, in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)5 (refs 4, 16,17,18,19 and 20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.

Place, publisher, year, edition, pages
2015. Vol. 520, no 7545, 78-81 p.
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-119834DOI: 10.1038/nature14296ISI: 000352027700040OAI: oai:DiVA.org:su-119834DiVA: diva2:848741
Available from: 2015-08-26 Created: 2015-08-26 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Structure and dynamics in solution – the core electron perspective
Open this publication in new window or tab >>Structure and dynamics in solution – the core electron perspective
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is based on theoretical studies of the molecular and electronic structure of solvated ions and molecules. Very detailed information of the system can be obtained from theoretical calculations, but a realistic model is dependent on an accurate computational method. Accurate calculations of core level electronic spectra, and evaluation of the modeling against experiments, are central parts of this work. The main tools used for characterization of the systems are high-level quantum chemistry and molecular dynamics simulations. 

Molecular components in solutions are involved in many key processes converting sunlight into chemical or electrical energy. Transition metal complexes, with their pronounced absorption in the visible light region of the electromagnetic spectrum, are core components in various energy conversion applications, and the iodide/triiodide redox couple is a commonly used electrolyte. The local structure of the electronic valence in transition metal complexes and the details of the solvation mechanisms of electrolyte solutions are investigated through the combination of computational modeling and core level spectroscopy. The studies of model systems show that interactions between the solute and solvent are important for the electronic structure, and knowledge of the details in model systems studied can be relevant for energy conversion applications. Furthermore, high-level quantum chemistry has been applied for interpreting time-resolved spectra, where the electronic structure of a metal complex is followed during a photoinduced chemical reaction in solution.

With advanced modeling in combination with recent experimental developments, more complex problems than previously addressed can be dissected.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2015. 64 p.
Keyword
quantum chemistry, RASSCF, molecular dynamics, x-ray spectroscopy, electrolyte solutions
National Category
Natural Sciences
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-119838 (URN)978-91-7649-258-1 (ISBN)
Public defence
2015-10-15, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 8: Manuscript.

Available from: 2015-09-23 Created: 2015-08-26 Last updated: 2015-09-11Bibliographically approved

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