Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)5 to Fe(CO)4EtOH

K Kunnus; I Josefsson; I Rajkovic; S Schreck; W Quevedo; M Beye; C Weniger; S Grübel; M Scholz; D Nordlund; W Zhang; R W Hartsock; K J Gaffney; W F Schlotter; J J Turner; B Kennedy; F Hennies; F M F de Groot; S Techert; M Odelius; Ph Wernet; A Föhlisch

doi:10.1063/1.4941602

Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)5 to Fe(CO)4EtOH

Struct Dyn. 2016 Feb 9;3(4):043204. doi: 10.1063/1.4941602. eCollection 2016 Jul.

Authors

K Kunnus, I Josefsson¹, I Rajkovic², S Schreck, W Quevedo³, M Beye³, C Weniger³, S Grübel², M Scholz², D Nordlund⁴, W Zhang⁵, R W Hartsock⁵, K J Gaffney⁵, W F Schlotter⁶, J J Turner⁶, B Kennedy³, F Hennies⁷, F M F de Groot⁸, S Techert, M Odelius¹, Ph Wernet³, A Föhlisch

Affiliations

¹ Department of Physics, Stockholm University , AlbaNova University Centre, 10691 Stockholm, Sweden.
² Max Planck Institute for Biophysical Chemistry , Am Fassberg 11, 37070 Göttingen, Germany.
³ Institute for Methods and Instrumentation for Synchrotron Radiation Research , Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
⁴ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Menlo Park, California 94025, USA.
⁵ PULSE Institute , SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
⁶ Linac Coherent Light Source, SLAC National Accelerator Laboratory , Menlo Park, California 94025, USA.
⁷ MAX-lab , P.O. Box 118, 221 00 Lund, Sweden.
⁸ Department of Chemistry, Utrecht University , Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.

Abstract

We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)5 in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)4 which are observed following a charge transfer photoexcitation of Fe(CO)5 as reported in our previous study [Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the (1)A1 state of Fe(CO)4. A sub-picosecond time constant of the spin crossover from (1)B2 to (3)B2 is rationalized by the proposed (1)B2 → (1)A1 → (3)B2 mechanism. Ultrafast ligation of the (1)B2 Fe(CO)4 state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the (3)B2 Fe(CO)4 ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via (1)B2 → (1)A1 → (1)A' Fe(CO)4EtOH pathway and the time scale of the (1)A1 Fe(CO)4 state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution.