title: Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives.
abstract: The valence-excited states of ferric and ferrous hexacyanide ions in aqueous solution were mapped by resonant inelastic X-ray scattering (RIXS) at the Fe L2,3 and N K edges. Probing of both the central Fe and the ligand N atoms enabled identification of the metal- and ligand-centered excited states, as well as ligand-to-metal and metal-to-ligand charge-transfer excited states. Ab initio calculations utilizing the RASPT2 method were used to simulate the Fe L2,3-edge RIXS spectra and enabled quantification of the covalencies of both occupied and empty orbitals of π and σ symmetry. We found that π back-donation in the ferric complex is smaller than that in the ferrous complex. This is evidenced by the relative amounts of Fe 3d character in the nominally 2π CN(-) molecular orbital of 7% and 9% in ferric and ferrous hexacyanide, respectively. Utilizing the direct sensitivity of Fe L3-edge RIXS to the Fe 3d character in the occupied molecular orbitals, we also found that the donation interactions are dominated by σ bonding. The latter was found to be stronger in the ferric complex, with an Fe 3d contribution to the nominally 5σ CN(-) molecular orbitals of 29% compared to 20% in the ferrous complex. These results are consistent with the notion that a higher charge at the central metal atom increases donation and decreases back-donation.
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Strasse 15, 12489 Berlin, Germany.|Institut für Physik und Astronomie, Universität Potsdam , Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany.
authors.forename: Kristjan
authors.initials: K
authors.lastname: Kunnus
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Wenkai
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , 75120 Uppsala, Sweden.
authors.forename: Mickaël G
authors.initials: MG
authors.lastname: Delcey
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , 75120 Uppsala, Sweden.
authors.forename: Rahul V
authors.initials: RV
authors.lastname: Pinjari
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
authors.forename: Piter S
authors.initials: PS
authors.lastname: Miedema
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Strasse 15, 12489 Berlin, Germany.|Institut für Physik und Astronomie, Universität Potsdam , Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany.
authors.forename: Simon
authors.initials: S
authors.lastname: Schreck
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
authors.forename: Wilson
authors.initials: W
authors.lastname: Quevedo
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Strasse 15, 12489 Berlin, Germany.|Institut für Physik und Astronomie, Universität Potsdam , Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Schröder
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Strasse 15, 12489 Berlin, Germany.|Institut für Physik und Astronomie, Universität Potsdam , Karl-Liebknecht-Strasse 24/25, 14476 Potsdam, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Föhlisch
authors.affiliation: PULSE Institute, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: Kelly J
authors.initials: KJ
authors.lastname: Gaffney
authors.affiliation: Department of Chemistry, Ångström Laboratory, Uppsala University , 75120 Uppsala, Sweden.
authors.forename: Marcus
authors.initials: M
authors.lastname: Lundberg
authors.affiliation: Department of Physics, Stockholm University, AlbaNova University Centre , 10691 Stockholm, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Odelius
authors.affiliation: Institute for Methods and Instrumentation for Synchrotron Radiation Research, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Albert-Einstein-Strasse 15, 12489 Berlin, Germany.
authors.forename: Philippe
authors.initials: P
authors.lastname: Wernet