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  Electronic Structure of a Weakly Antiferromagnetically Coupled MnIIMnIII Model Relevant to Manganese Proteins: A Combined EPR, 55Mn-ENDOR, and DFT Study

Cox, N., Ames, W., Epel, B., Kulik, L. V., Rapatskiy, L., Neese, F., et al. (2011). Electronic Structure of a Weakly Antiferromagnetically Coupled MnIIMnIII Model Relevant to Manganese Proteins: A Combined EPR, 55Mn-ENDOR, and DFT Study. Inorganic Chemistry, 50(17), 8238-8251. doi:10.1021/ic200767e.

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 Creators:
Cox, Nicholas1, Author              
Ames, William1, 2, Author              
Epel, Boris1, Author              
Kulik, Leonid V.3, Author
Rapatskiy, Leonid1, Author              
Neese, Frank2, 4, Author              
Messinger, Johannes5, Author
Wieghardt, Karl6, Author              
Lubitz, Wolfgang1, Author              
Affiliations:
1Research Department Lubitz, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society, ou_3023878              
2Lehrstuhl für Theoretische Chemie, Institut für Physikalische und Theoretische Chemie, Universität Bonn, Wegelerstrasse 12, D-53115 Bonn, Germany, ou_persistent22              
3Institute of Chemical Kinetics and Combustion, Institutskaya 3, 630090 Novosibirsk, Russia, ou_persistent22              
4Research Department Neese, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society, ou_3023879              
5Department of Chemistry, Kemiskt Biologiskt Centrum (KBC), Umeå University, S-90187 Umeå, Sweden, ou_persistent22              
6Research Department Wieghardt, Max Planck Institute for Bioinorganic Chemistry, Max Planck Society, ou_3023881              

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 Abstract: An analysis of the electronic structure of the [MnIIMnIII(μ-OH)-(μ-piv)2(Me3tacn)2](ClO4)2 (PivOH) complex is reported. It displays features that include: (i) a ground 1/2 spin state; (ii) a small exchange (J) coupling between the two Mn ions; (iii) a mono-μ-hydroxo bridge, bis-μ-carboxylato motif; and (iv) a strongly coupled, terminally bound N ligand to the MnIII. All of these features are observed in structural models of the oxygen evolving complex (OEC). Multifrequency electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) measurements were performed on this complex, and the resultant spectra simulated using the Spin Hamiltonian formalism. The strong field dependence of the 55Mn-ENDOR constrains the 55Mn hyperfine tensors such that a unique solution for the electronic structure can be deduced. Large hyperfine anisotropy is required to reproduce the EPR/ENDOR spectra for both the MnII and MnIII ions. The large effective hyperfine tensor anisotropy of the MnII, a d5 ion which usually exhibits small anisotropy, is interpreted within a formalism in which the fine structure tensor of the MnIII ion strongly perturbs the zero-field energy levels of the MnIIMnIII complex. An estimate of the fine structure parameter (d) for the MnIII of −4 cm–1 was made, by assuming the intrinsic anisotropy of the MnII ion is small. The magnitude of the fine structure and intrinsic (onsite) hyperfine tensor of the MnIII is consistent with the known coordination environment of the MnIII ion as seen from its crystal structure. Broken symmetry density functional theory (DFT) calculations were performed on the crystal structure geometry. DFT values for both the isotropic and the anisotropic components of the onsite (intrinsic) hyperfine tensors match those inferred from the EPR/ENDOR simulations described above, to within 5%. This study demonstrates that DFT calculations provide reliable estimates for spectroscopic observables of mixed valence Mn complexes, even in the limit where the description of a well isolated S = 1/2 ground state begins to break down.

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Language(s): eng - English
 Dates: 2011-04-132011-08-112011-09-05
 Publication Status: Published in print
 Pages: 14
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/ic200767e
 Degree: -

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Title: Inorganic Chemistry
  Abbreviation : Inorg. Chem.
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 50 (17) Sequence Number: - Start / End Page: 8238 - 8251 Identifier: ISSN: 0020-1669
CoNE: https://pure.mpg.de/cone/journals/resource/0020-1669