A R T I C L E S
Novozhilova et al.
Infrared Spectroscopy and Photochemistry. The methodology
employed for the FT-IR experiments has been described previously.47
Thus, FT-IR measurements were obtained on a BioRad FTS40A IR
spectrometer equipped with an MCT detector. The spectral resolution
was 1 cm-1. The samples consisted of freshly prepared KBr pellets
(approximately 1 mm thick) of the compounds, and these samples were
mounted in an IR transmission cell. The cell was evacuated to ∼10-7
bar using a turbo-molecular pump. The samples were cooled to 11 K
using an APD Helitran LT-3-110 optical cryostat equipped with NaCl
windows and connected to a liquid N2 tank, and the sample temperature
was controlled to within 1 K using a Scientific Instruments 9620-R-
1-1 temperature controller.
criterion were set to 10-8 and 10-10, respectively. Graphics were done
with MOLEKEL4.1 software.60 The electron localization function (ELF)
was calculated with program DGrid v2.4.61
Results and Discussion
X-ray Crystal Structures of (por)Fe(NO2)-Containing
Compounds. Scheidt and co-workers have characterized, by
X-ray crystallography, a number of (por)Fe(NO)(NO2) com-
pounds.62 The structure of the title compound (TPP)Fe(NO)-
(NO2) suffered from severe disorder, limiting the usefulness of
the metrical data. However, accurate structural results for
different crystal forms of the picket-fence derivative (TpivPP)-
Fe(NO)(NO2) show N-binding of both the nitrosyl and the nitro
ligands to the iron center. The plane of the nitrite ion essentially
bisects adjacent pairs of Fe-N(por) bonds in these derivatives,
and the Fe atoms are displaced by 0.09-0.15 Å from the 24-
atom mean porphyrin planes toward the nitrosyl ligands. In all
heme and heme-model nitrite structures published to date, the
NO2 group is N-bound to the metal center. Examples include
the ferrous complexes [(TpivPP)Fe(NO2)]-63,64 and [(TpivPP)Fe-
(NO2)(L)]- (L ) CO,65 PMS,63 Py,63 NO),66 and the ferric
Light from a 300 W Xe arc lamp passed through a heat absorbing
water filter and a 300-500 nm broadband filter was used for the
irradiation, and the samples were mounted at 45° to both the IR beam
and the irradiating light.
The sample was irradiated at various temperatures (11, 200, and
250 K), and the infrared spectra at those temperatures were recorded
just prior to irradiation and then after ∼10 min irradiation. The decay
of the metastable species was investigated by halting the irradiation,
warming the sample to higher temperature (e.g., 50, 200, 250, 295 K),
holding the sample at the specified higher temperature for ∼5 min,
cooling the sample back to the initial temperature used for the irradiation
experiment, and re-recording the IR spectrum.
compounds
[(TpivPP)Fe(NO2)2]-,67
[(TpivPP)Fe(NO2)-
(SC6F4H)]-,68 and [(TpivPP)Fe(NO2)(L) (L ) HIm,69 Py69,70).
To the best of our knowledge based on the literature and an
only three heme proteins with bound nitrite have been character-
ized by X-ray crystallography, and these are the nitrite complex
of reduced cytochrome cd1 nitrite reductase from Paracoccus
pantotropha,71 the nitrite complex of ferric cytochrome c nitrite
reductase from Wolinella succinogenes,72 and the nitrite complex
of ferric E. coli sulfite reductase hemoprotein.73 All three protein
structures also show N-binding of the NO2 group to the iron
centers. In fact, such N-binding of NO2 groups to iron porphyrins
and heme appears to dominate.28 The only exceptions where
O-binding has been established are those involving a disordered
component of [(TpivPP)Fe(NO2)(NO)]-66 and that of a recently
determined nitrito complex of myoglobin.74 As mentioned
earlier, the other group 8 compounds (por)M(NO)(ONO) (M
) Ru,29-31 Os32) possess O-bound nitrito ligands in their ground-
state X-ray crystal structures.
Computational Details. All calculations were carried out in the gas
phase with the Amsterdam Density Functional (ADF2004.01) pro-
gram.48-50 The calculations were performed using the nonlocal func-
tional of Becke51 for exchange and Lee-Yang-Parr52 for correlation.
The frozen core approximation was utilized with (1s2s2p)10 core on
Fe, and (1s)2 core on C, N, and O atoms. The relativistic correction
was introduced with the zeroth-order regular approximation (ZORA).53-56
A triple-ú basis set with 4p function (TZP) was used on Fe, whereas
a double-ú quality basis set with one polarization function (DZP) was
employed for all other elements. The SCF convergence criterion for
the maximum element of the Fock matrix was set to 10-8, while
convergence criterion on the gradients was set to 4 × 10-4 Hartree/Å
(as compared to the default setting of 10-2 Hartree/Å). IR frequency
calculations were performed for all geometries in the gas phase. In
frequency calculations, the integration accuracy was set to 8 significant
digits and a “smooth freezecell” feature was applied to improve the
quality of the Hessian (second derivative matrix). No scaling correction
was introduced to the calculated frequencies. Time-dependent DFT (TD-
DFT)57-59 calculations of vertical excitation energies were carried out
on the ground-state optimized geometry with the asymptotically correct
“statistical-average-of-orbital potentials” (SAOP) using an all-electron
TZP basis set on Fe and all-electron DZP basis set on all other atoms.
The Davidson algorithm was used, in which the error tolerances in the
square of the excitation energies and the trial-vector orthonormality
(60) Flukiger, P.; Luthi, H. P.; Portmann, S.; Weber, J. Swiss Center for Scientific
Computing: Manno, Switzerland, 2000-2001.
(61) Kohout, M. DGrid, Version 2.4; Max-Planck Institute for Chemical Physics
of Solids: Dresden, Germany, 2004.
(62) Ellison, M. K.; Schulz, C. E.; Scheidt, W. R. Inorg. Chem. 1999, 38, 100-
108.
(63) Nasri, H.; Ellison, M. K.; Krebs, C.; Huynh, B. H.; Scheidt, W. R. J. Am.
Chem. Soc. 2000, 122, 10795-10804.
(47) Kovalevsky, A. Y.; Bagley, K. A.; Cole, J. M.; Coppens, P. Inorg. Chem.
2003, 42, 140-147.
(64) Nasri, H.; Wang, Y.; Huynh, B. H.; Scheidt, W. R. J. Am. Chem. Soc.
1991, 113, 717-719.
(48) te Velde, G.; Bickelhaupt, F. M.; van Gisbergen, S. J. A.; Fonseca Guerra,
C.; Baerends, E. J.; Snijders, J. G.; Zeigler, T. J. Comput. Chem. 2001, 22,
931-967.
(65) Nasri, H.; Ellison, M. K.; Shang, M.; Schultz, C. E.; Scheidt, W. R. Inorg.
Chem. 2004, 43, 2932-2942.
(49) Fonseca Guerra, C.; Snijders, J. G.; te Velde, G.; Baerends, E. J. Theor.
Chem. Acc. 1998, 99, 391.
(66) Nasri, H.; Ellison, M. K.; Chen, S.; Huynh, B. H.; Scheidt, W. R. J. Am.
Chem. Soc. 1997, 119, 6274-6283.
(50) Baerends, E. J.; et al. ADF 2004.01; SCM, Theoretical Chemistry; http://
(51) Becke, A. D. Phys. ReV. A 1988, 38, 3098.
(67) Nasri, H.; Goodwin, J. A.; Scheidt, W. R. Inorg. Chem. 1990, 29, 185-
191.
(68) Nasri, H.; Haller, K. J.; Wang, Y.; Huynh, B. H.; Scheidt, W. R. Inorg.
Chem. 1992, 31, 3459-3467.
(52) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785-789.
(53) Chang, C.; Pelissier, M.; Durand, M. Phys. Scr. 1986, 34, 394-404.
(54) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1993, 99,
4597-4610.
(69) Nasri, H.; Wang, Y.; Huynh, B. H.; Walker, F. A.; Scheidt, W. R. Inorg.
Chem. 1991, 30, 1483-1489.
(70) Cheng, L.; Powell, D. R.; Khan, M. A.; Richter-Addo, G. B. Chem.
Commun. 2000, 2301-2302.
(55) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Chem. Phys. 1994, 101,
9783-9792.
(71) Williams, P. A.; Fu¨lo¨p, V.; Garman, E. F.; Saunders, N. F. W.; Ferguson,
S. J.; Hajdu, J. Nature 1997, 389, 406-412.
(56) van Lenthe, E.; van Leeuwen, R.; Baerends, E. J.; Snijders, J. G. Int. J.
Quantum Chem. 1996, 57, 281-293.
(72) Einsle, O.; Messerschmidt, A.; Huber, R.; Kroneck, P. M. H.; Neese, F. J.
Am. Chem. Soc. 2002, 124, 11737-11745.
(57) van Gisbergen, S. J. A.; Kootstra, F.; Schipper, P. R. T.; Gritsenko, O. V.;
Snijders, J. G.; Baerends, E. J. Phys. ReV. A 1998, 57, 2556-2571.
(58) Jamorski, C.; Casida, M. E.; Salahub, D. R. J. Chem. Phys. 1996, 104,
5134-5147.
(73) Crane, B. R.; Siegel, L. M.; Getzoff, E. D. Biochemistry 1997, 36, 12120-
12137.
(74) Copeland, D. M.; West, A.; Soares, A.; Richter-Addo, G. B., manuscript
in preparation.
(59) Bauernschmitt, R.; Ahlrichs, R. Chem. Phys. Lett. 1996, 256, 454-464.
9
2096 J. AM. CHEM. SOC. VOL. 128, NO. 6, 2006