Abstract
We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)2]2+ (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the 5T2/3T1 crossing point and stabilizing the latter as the lowest energy excited state. Kα and Kβ X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the 5T2 state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of â0.18 Å for a 5T2 state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited 5T2 state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin 1A1 ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.
| Original language | English |
|---|---|
| Pages (from-to) | 9341-9350 |
| Number of pages | 10 |
| Journal | Inorganic Chemistry |
| Volume | 58 |
| Issue number | 14 |
| DOIs | |
| Publication status | Published - 2019 Jun 26 |
Bibliographical note
Funding Information:This work is financed by the European XFEL, by the Deutsche Forschungsgemeinschaft (DFG) via SFB 925, project A4 (T.A.A.), and by the Hamburg Centre for Ultrafast Imaging (CUI). A.B. acknowledges support from the International Max Planck Research School for Ultrafast Imaging and Structural Dynamics (IMPRS-UFAST), and we acknowledge the European Cluster of Advanced Laser Light Sources (EUCALL) within work packages PUCCA (C.B.), which has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No 654220. W.G. further acknowledges partial financial support from the National Science Centre (NCN) in Poland under SONATA BIS 6 Grant No. 2016/22/E/ST4/00543. Work by A.M.M., G.D., S.H.S., L.Y., H.C. and R.W.S. was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Chemical Sciences, Geosciences, and Biosciences Division. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. É.B., Z.N., D.S.Sz. and G.V. were supported by the “Lendület” (Momentum) Program of the Hungarian Academy of Sciences (LP2013-59), the Government of Hungary, and the European Regional Development Fund under Grant VEKOP-2.3.2-16-2017-00015, and the National Research, Development and Innovation Fund (NKFIH FK 124460). Z.N. acknowledges support from the Bolyai Fellowship of the Hungarian Academy of Sciences. E.J., C.L., and S.M. acknowledge support from the U.S. Army Research Office under Contract W911NF-15-1-0124. The research leading to the presented results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA Grant Agreement No. 609405 (M.P., COFUNDPostdocDTU) and the Independent Research Fund (8021-00347B), Denmark (M.P.). Figure 1 has been created with MarvinSketch and Inkscape. We are grateful to the staff of 7-ID from the APS for help during the experiment and we thank X. Zhang for support with the peristaltic pump, Diego Casa for the loan of an analyzer crystal and A. Guda for fruitful discussions. Finally, J.K.M. gratefully acknowledges support from the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy though Grant No. DE-FG02-01ER15282.
Funding Information:
This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. E?.B., Z.N., D.S.Sz. and G.V. were supported by the "Lendu?let" (Momentum) Program of the Hungarian Academy of Sciences (LP2013-59) the Government of Hungary, and the European Regional Development Fund under Grant VEKOP-2.3.2-16-2017-00015, and the National Research Development and Innovation Fund (NKFIH FK 124460). Z.N. acknowledges support from the Bolyai Fellowship of the Hungarian Academy of Sciences. E.J., C.L., and S.M. acknowledge support from the U.S. Army Research Office under Contract W911NF-15-1-0124. The research leading to the presented results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA Grant Agreement No. 609405 (M.P., COFUNDPostdocDTU) and the Independent Research Fund (8021-00347B), Denmark (M.P.). Figure 1 has been created with MarvinSketch and Inkscape. We are grateful to the staff of 7-ID from the APS for help during the experiment and we thank X. Zhang for support with the peristaltic pump, Diego Casa for the loan of an analyzer crystal and A. Guda for fruitful discussions. Finally, J.K.M. gratefully acknowledges support from the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy though Grant No. DE-FG02-01ER15282.
Publisher Copyright:
© 2019 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry
- Inorganic Chemistry