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Title: Probing the Impact of Solvation on Photoexcited Spin Crossover Complexes with High-Precision X-ray Transient Absorption Spectroscopy

Investigating the photoinduced electronic and structural response of bistable molecular building blocks incorporating transition metals in solution phase constitutes a necessary stepping stone for steering their properties towards applications and perfomance optimizations. Here, this paper presents a detailed X-ray transient absorption (XTA) spectroscopy study of a prototypical spin crossover (SCO) complex [Fe II(mbpy) 3] 2+ (where mbpy=4,4’-dimethyl-2,2’-bipyridine) with a [Fe IIN 6] first coordination shell in water (H 2O) and acetonitrile (CH 3CN). The unprecedented data quality of the XTA spectra together with the direct fitting of the difference spectra in k space using a large number of scattering paths enables resolving the subtle difference in the photoexcited structures of an Fe II complex in two solvents for the first time. Also, compared to the low spin (LS) 1A 1 state, the average Fe-N bond elongations for the photoinduced high spin (HS) 5T 2 state are found to be 0.181 ± 0.003 Å in H 2O and 0.199 ± 0.003 Å in CH 3CN. This difference in structural response is attributed to ligand-solvent interactions that are stronger in H 2O than in CH 3CN for the HS excited state. Our studies demonstrate that, although the metal center of [Fe II(mbpy)more » 3] 2+ could have been expected to be rather shielded by the three bidentate ligands with quasi-octahedral-coordination, the ligand field strength in the HS excited state is nevertheless indirectly affected by solvation that modifies the charge distribution within the Fe-N covalent bonds. More generally, this work highlights the importance of including solvation effects in order to develop a generalized understanding of the spin-state switching at the atomic level.« less
 [1] ;  [2] ; ORCiD logo [3] ;  [4] ;  [5] ; ORCiD logo [1]
  1. Argonne National Lab. (ANL), Argonne, IL (United States). X-ray Science Division
  2. Tianjin Polytechnic University (China). State Key Laboratory of Hollow Fibre Membrane Materials and Processes, School of Environmental and Chemical Engineering
  3. University of Geneva (Switzerland). Dept. of Physical Chemistry
  4. Argonne National Lab. (ANL), Argonne, IL (United States). Center for Nanoscale Materials
  5. ELI-ALPS, ELI-HU Non-Profit Ltd. (Hungary); Deutsches Elektronen Synchrotron (DESY), Hamburg (Germany). Attosecond Science Group
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 48; Journal ID: ISSN 0002-7863
American Chemical Society (ACS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier: