Characterization of a genuine iron(V)-nitrido species by nuclear resonant vibrational spectroscopy coupled to density functional calculations.
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.
Petrenko
Taras
T
Institut für Physikalische und Theoretische Chemie, Wegelerstr. 12, D-53115 Bonn, Germany.
DeBeer George
Serena
S
Aliaga-Alcalde
Núria
N
Bill
Eckhard
E
Mienert
Bernd
B
Xiao
Yuming
Y
Guo
YiSong
Y
Sturhahn
Wolfgang
W
Cramer
Stephen P
SP
Wieghardt
Karl
K
Neese
Frank
F
D007501:Iron / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D017672:Nitrogen Compounds / Q000737:chemistry*
D017672:Nitrogen Compounds; C066318:perferryl iron; D007501:Iron