title: Characterization of a genuine iron(V)-nitrido species by nuclear resonant vibrational spectroscopy coupled to density functional calculations.
abstract: The characterization of high-valent iron species is of interest due to their relevance to biological reaction mechanisms. Recently, we have synthesized and characterized an [Fe(V)-nitrido-cyclam-acetato]+ complex, which has been characterized by Mössbauer, magnetic susceptibility data, and XAS spectroscopies combined with DFT calculations (Aliaga-Alcade, N.; DeBeer George, S.; Bill, E.; Wieghardt, K.; Neese, F. Angew. Chem., Int. Ed. 2005, 44, 2908-2912). The results of this study indicated that the [Fe(V)-nitrido-cyclam-acetato]+ complex is an unusual d3 system with a nearly orbitally degenerate S=1/2 ground state. Although the calculations predicted fairly different Fe-N stretching frequencies for the S=1/2 and the competing S=3/2 ground states, a direct experimental determination of this important fingerprint quantity was missing. Here we apply synchrotron-based nuclear resonance vibrational scattering (NRVS) to characterize the Fe-N stretching frequency of an Fe(V)-nitrido complex and its Fe(III)-azide precursor. The NRVS data show a new isolated band at 864 cm(-1) in the Fe(V)-nitrido complex that is absent in the precursor. The NRVS spectra are fit and simulated using a DFT approach, and the new feature is unambiguously assigned to a Fe(V)-N stretch. The calculated Fe-N stretching frequency is too high by approximately 75 cm(-1). Anharmonic contributions to the Fe-N stretching frequency have been evaluated and have been found to be small (-5.5 cm(-1)). The NRVS data provided a unique opportunity to obtain this vibrational information, which had eluded characterization by more traditional vibrational spectroscopies.
authors: Institut für Physikalische und Theoretische Chemie, Wegelerstr. 12, D-53115 Bonn, Germany.
authors: Taras
authors: T
authors: Petrenko
authors: Serena
authors: S
authors: DeBeer George
authors: Núria
authors: N
authors: Aliaga-Alcalde
authors: Eckhard
authors: E
authors: Bill
authors: Bernd
authors: B
authors: Mienert
authors: Yuming
authors: Y
authors: Xiao
authors: YiSong
authors: Y
authors: Guo
authors: Wolfgang
authors: W
authors: Sturhahn
authors: Stephen P
authors: SP
authors: Cramer
authors: Karl
authors: K
authors: Wieghardt
authors: Frank
authors: F
authors: Neese
mesh_terms: D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D017672:Nitrogen Compounds / Q000737:chemistry*
chemical_list: D017672:Nitrogen Compounds; C066318:perferryl iron; D007501:Iron