Photodissociation of ironpentacarbonyl acts as a carbonmonoxide geyser

In excited state molecular dynamics simulations, we have resolved the early steps in the photodissociation of ironpentacarbonyl. The mechanism of CO release involves periodic transitions between the initially excited metal-to-ligand charge-transfer state and dissocative metal--centered states.
Photodissociation of ironpentacarbonyl acts as a carbonmonoxide geyser

Transition metal complexes can be used as efficient catalysts for the transformation of solar light energy into chemical energy. They possess easily accessible close-lying electronic states that lead to a plethora of complex and ultrafast photochemical processes during the first steps of energy conversion. In theoretical simulations, a collaboration of scientists at Stockholm University and Uppsala University has now followed the ultrafast non-adiabatic dynamics in the photodissociation of the prototypical transition-metal complex ironpentacarbonyl. The coupled motions of atoms and electrons they see on the time scale of femtoseconds (one femtosecond = 10 -15 seconds) has been challenging to characterize theoretically to date. In their study they resolve the initial events and find that a bright metal-to-ligand charge-transfer transition induces synchronous Fe-CO oscillations, followed by sequential transitions to dissociative metal-centered excited states. This leads to periodically recurring releases of carbonmonoxide, very much like the periodic ejection of water in a geyser. The discovery of this periodic ejections of carbonmonoxide is important as it predicts that the resulting catalytically active irontetracarbonyl fragment also is created periodically and on femtosecond time scales.

The work was lead by Ambar Banerjee and Michael Odelius at Fysikum, Stockholm University. The lead author Ambar Banerjee says that "This detailed mechanistic insight will have to be explored experimentally, and might be an essential ingredient in understanding photophysics and photochemistry of transition metal carbonyls. In the end it could give a decisive handle on improved design of photocatalysts”. The investigation was performed in a collaboration of scientists from the Department of Physics at Stockholm University and from the Department of Physics and Astronomy at Uppsala University.

Potential energy surfaces of electronic states of interest displayed along selected Fe-C coordinates.
Photoexcitation of the ironpentacarbonyl complex from the electronic ground state (GS) into a metal-to-ligand charge-transfer (MLCT) state triggers Fe-CO oscillations, which after electronic rearrangement into a metal-centered state (MC) lead to periodic bursts of carbonmonooxide (CO).

The study is published in a recent issue of Nature Communication DOI:10.1038/s41467-022-28997-z
Photoinduced bond oscillations in ironpentacarbonyl give delayed synchronous bursts of carbonmonoxide release Ambar Banerjee, Michael R. Coates, Markus Kowalewski, Hampus Wikmark, Raphael M. Jay, Philippe Wernet, and Michael Odelius

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