title: In search of metal hydrides: an X-ray absorption and emission study of [NiFe] hydrogenase model complexes.
abstract: Metal hydrides are invoked as important intermediates in both chemical and biological H2 production. In the [NiFe] hydrogenase enzymes, pulsed EPR and high-resolution crystallography have argued that the hydride interacts primarily at the Ni site. In contrast, in [NiFe] hydrogenase model complexes, it is observed that the bridging hydride interacts primarily with the Fe. Herein, we utilize a combination of Ni and Fe X-ray absorption (XAS) and emission (XES) spectroscopies to examine the contribution of the bridging hydride to the observed spectral features in [(dppe)Ni(μ-pdt)(μ-H)Fe(CO)3](+). The corresponding data on (dppe)Ni(μ-pdt)Fe(CO)3 are used as a reference for the changes that occur in the absence of a hydride bridge. For further interpretation of the observed spectral features, all experimental spectra were calculated using a density functional theory (DFT) approach, with excellent agreement between theory and experiment. It is found that the iron valence-to-core (VtC) XES spectra reveal clear signatures for the presence of a Fe-H interaction in the hydride bridged model complex. In contrast, the Ni VtC XES spectrum largely reflects changes in the local Ni geometry and shows little contribution from a Ni-H interaction. A stepwise theoretical analysis of the hydride contribution and the Ni site symmetry provides insights into the factors, which govern the different metal-hydride interactions in both the model complexes and the enzyme. Furthermore, these results establish the utility of two-color XES to reveal important insights into the electronic structure of various metal-hydride species.
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hugenbruch
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de and The Ohio State University, Department of Chemistry and Biochemistry, 100 West 18th Avenue, Columbus, OH 43210-1173, USA.
authors.forename: Hannah S
authors.initials: HS
authors.lastname: Shafaat
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de and Heriot-Watt University, Institute of Chemical Sciences, Edinburgh EH14 4AS, UK.
authors.forename: Tobias
authors.initials: T
authors.lastname: Krämer
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de and Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, Utrecht 3584 CG, The Netherlands.
authors.forename: Mario Ulises
authors.initials: MU
authors.lastname: Delgado-Jaime
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de.
authors.forename: Katharina
authors.initials: K
authors.lastname: Weber
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de.
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lubitz
authors.affiliation: Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34 - 36, Mülheim a. d. Ruhr, D-45470, Germany. serena.debeer@cec.mpg.de and Cornell University, Department of Chemistry and Chemical Biology, Ithaca, New York 14853, USA.
authors.forename: Serena
authors.initials: S
authors.lastname: DeBeer
mesh_terms: D006859:Hydrogen / Q000737:chemistry*; D006864:Hydrogenase / Q000737:chemistry*; D008958:Models, Molecular; D056928:X-Ray Absorption Spectroscopy
chemical_list: D006859:Hydrogen; C043296:nickel-iron hydrogenase; D006864:Hydrogenase