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  The Protonation States of Oxo-Bridged MnIV Dimers Resolved by Experimental and Computational Mn K Pre-Edge X-ray Absorption Spectroscopy

Krewald, V., Lasalle-Kaiser, B., Boron III, T. T., Pollock, C. J., Kern, J., Beckwith, M. A., et al. (2013). The Protonation States of Oxo-Bridged MnIV Dimers Resolved by Experimental and Computational Mn K Pre-Edge X-ray Absorption Spectroscopy. Inorganic Chemistry, 52(22), 12904-12914. doi:10.1021/ic4008203.

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Krewald, Vera1, Author              
Lasalle-Kaiser, Benedikt2, Author
Boron III, Thaddeus T.3, Author
Pollock, Chistopher J.1, Author              
Kern, Jan2, 4, Author
Beckwith, Martha. A.1, 5, Author              
Yachanrda, Vittal K.2, Author
Pecoraro, Vincent L.3, Author
Yano, Junko2, Author
Neese, Frank1, Author              
DeBeer, Serena1, 5, Author              
1Research Department Neese, Max Planck Institute for Chemical Energy Conversion, Max Planck Society, ou_3023886              
2Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States, ou_persistent22              
3Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States, ou_persistent22              
4SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States, ou_persistent22              
5Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States, ou_persistent22              


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 Abstract: In nature, the protonation of oxo bridges is a commonly encountered mechanism for fine-tuning chemical properties and reaction pathways. Often, however, the protonation states are difficult to establish experimentally. This is of particular importance in the oxygen evolving complex of photosystem II, where identification of the bridging oxo protonation states is one of the essential requirements toward unraveling the mechanism. In order to establish a combined experimental and theoretical protocol for the determination of protonation states, we have systematically investigated a series of Mn model complexes by Mn K pre-edge X-ray absorption spectroscopy. An ideal test case for selective bis-μ-oxo-bridge protonation in a Mn dimer is represented by the system [MnIV2(salpn)2(μ-OHn)2]n+. Although the three species [MnIV2(salpn)2(μ-O)2], [MnIV2(salpn)2(μ-O)(μ-OH)]+ and [MnIV2(salpn)2(μ-OH)2]2+ differ only in the protonation of the oxo bridges, they exhibit distinct differences in the pre-edge region while maintaining the same edge energy. The experimental spectra are correlated in detail to theoretically calculated spectra. A time-dependent density functional theory approach for calculating the pre-edge spectra of molecules with multiple metal centers is presented, using both high spin (HS) and broken symmetry (BS) electronic structure solutions. The most intense pre-edge transitions correspond to an excitation of the Mn 1s core electrons into the unoccupied orbitals of local eg character (dz2 and dxy based in the chosen coordinate system). The lowest energy experimental feature is dominated by excitations of 1s-α electrons, and the second observed feature is primarily attributed to 1s-β electron excitations. The observed energetic separation is due to spin polarization effects in spin-unrestricted density functional theory and models final state multiplet effects. The effects of spin polarization on the calculated Mn K pre-edge spectra, in both the HS and BS solutions, are discussed in terms of the strength of the antiferromagnetic coupling and associated changes in the covalency of Mn–O bonds. The information presented in this paper is complemented with the X-ray emission spectra of the same compounds published in an accompanying paper. Taken together, the two studies provide the foundation for a better understanding of the X-ray spectroscopic data of the oxygen evolving complex (OEC) in photosystem II.


Language(s): eng - English
 Dates: 2013-04-032013-10-252013-11-18
 Publication Status: Published in print
 Pages: 11
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/ic4008203
 Degree: -



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Title: Inorganic Chemistry
  Abbreviation : Inorg. Chem.
Source Genre: Journal
Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 52 (22) Sequence Number: - Start / End Page: 12904 - 12914 Identifier: ISSN: 0020-1669
CoNE: https://pure.mpg.de/cone/journals/resource/0020-1669