Structural, Magnetic, and Dynamic Characterization of the (dxz,dyz)4(dxy)1 Ground-State Low-Spin Iron(III) Tetraphenylporphyrinate Complex [(p-TTP)Fe(2,6-XylylNC)2]CF3SO3

Simonneaux, Gérard; Schünemann, Volker; Morice, Christophe; Carel, Laurence; Toupet, Loı̈c; Winkler, H.; Trautwein, Alfred X.; Walker, F. Ann

doi:10.1021/ja994190t

Cited by 86 publications

(118 citation statements)

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“…3 possible; both the d xy and a 2u orbitals in D 4h complexes are represented as b 2 in ruffled D 2d complexes [14,15]. In fact, the X-ray crystallographic data have revealed that almost all the low-spin complexes adopting the (d xz , d yz ) 4 (d xy ) 1 ground state have exhibited the ruffled porphyrin core [12,[16][17][18]. The d xy -a 2u interaction in ruffled complexes induces a sizable amount of spin densities on the meso carbon atoms since the a 2u orbital has large coefficient on these atoms.…”

Section: Spectroscopic Methods To Determine the Electronic Ground Statesmentioning

confidence: 99%

Electronic ground states of low-spin iron(III) porphyrinoids

Nakamura

Ohgo

Ikezaki

2008

Journal of Inorganic Biochemistry

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Section: Spectroscopic Methods To Determine the Electronic Ground Statesmentioning

confidence: 99%

Electronic ground states of low-spin iron(III) porphyrinoids

Nakamura

Ohgo

Ikezaki

2008

Journal of Inorganic Biochemistry

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“…8,46,63 In line with this, the pyrrole-H chemical shift is close to its diamagnetic value, or even somewhat more positive, while the meso-phenyl-H shift differences, δ m -δ p , and δ m -δ o , are both large and positive (+12 to +19 ppm at ambient temperatures) (Figure 11), indicating large positive spin density at the meso-carbons 8,38,46,59,63 (Table 1). In fact, it is interesting that the saddled complex, octaethyltetraphenylporphyrinatoiron(III) bis(t-butylisocyanide), which will be discussed in more detail elsewhere, 64 has much smaller meso-phenyl shifts because of the reduced possibility of ruffling of the porphyrinate ring.…”

Section: H Nmr Spectroscopy Of Paramagnetic Iron Macrocycle Complexesmentioning

confidence: 99%

Pulsed EPR and NMR Spectroscopy of Paramagnetic Iron Porphyrinates and Related Iron Macrocycles: How To Understand Patterns of Spin Delocalization and Recognize Macrocycle Radicals

2003

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Pulsed EPR spectroscopic techniques, including ESEEM (electron spin echo envelope modulation) and pulsed ENDOR (electron−nuclear double resonance), are extremely useful for determining the magnitudes of the hyperfine couplings of macrocycle and axial ligand nuclei to the unpaired electron(s) on the metal as a function of magnetic field orientation relative to the complex. These data can frequently be used to determine the orientation of the g-tensor and the distribution of spin density over the macrocycle, and to determine the metal orbital(s) containing unpaired electrons and the macrocycle orbital(s) involved in spin delocalization. However, these studies cannot be carried out on metal complexes that do not have resolved EPR signals, as in the case of paramagnetic evenelectron metal complexes. In addition, the signs of the hyperfine couplings, which are not determined directly in either ESEEM or pulsed ENDOR experiments, are often needed in order to translate hyperfine couplings into spin densities. In these cases, NMR isotropic (hyperfine) shifts are extremely useful in determining the amount and sign of the spin density at each nucleus probed. For metal complexes of aromatic macrocycles such as porphyrins, chlorins, or corroles, simple rules allow prediction of whether spin delocalization occurs through σ or π bonds, and whether spin density on the ligands is of the same or opposite sign as that on the metal. In cases where the amount of spin density on the macrocycle and axial ligands is found to be too large for simple metal−ligand spin delocalization, a macrocycle radical may be suspected. Large spin density on the macrocycle that is of the same sign as that on the metal provides clear evidence of either no coupling or weak ferromagnetic coupling of a macrocycle radical to the unpaired electron(s) on the metal, while large spin density on the macrocycle that is of opposite sign to that on the metal provides clear evidence of antiferromagnetic coupling. The latter is found in a few iron porphyrinates and in most iron corrolates that have been reported thus far. It is now clear that iron corrolates are remarkably noninnocent complexes, with both negative and positive spin density on the macrocycle: for all chloroiron corrolates reported thus far, the balance of positive and negative spin density yields −0.65 to −0.79 spin on the macrocycle. On the other hand, for phenyliron corrolates, the balance of spin density on the macrocycle is zero, to within the accuracy of the calculations (Zakharieva, O.; Schünemann, V.; Gerdan, M.; Licoccia, S.; Cai, S.; Walker, F. A.; Trautwein, A. X. J. Am. Chem. Soc. 2002, 124, 6636−6648), although both negative and positive spin densities are found on the individual atoms. DFT calculations are invaluable in providing calculated spin densities at positions that can be probed by 1 H NMR spectroscopy, and the good agreement between calculated spin densities and measured hyperfine shifts at these positions leads to increased confidence in the calculated spin densities at position...

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“…These findings led to the hypothesis that at ambient temperatures ferrihemes axially coordinated by a peroxide ligand are likely to have the (d xy ) 1 electronic configuration [102]. Significant about this electronic configuration is the fact that ferric porphyrinates possessing an unpaired electron in the d xy orbital are significantly ruffled and place a relatively large amount of spin and electron density at the porphyrin meso carbons [15,89,91,104] (see Fig. 10).…”

Section: Nmr Chemical Shifts Of Quaternary Carbons and Heme Electromentioning

confidence: 99%

Recent developments in the 13 C NMR spectroscopic analysis of paramagnetic hemes and heme proteins

Rivera

Caignan

2004

Analytical and Bioanalytical Chemistry

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Despite the wealth of information that has been obtained from the study of paramagnetic hemes and heme proteins by 1H NMR spectroscopy, there are certain limitations imposed by the nature of paramagnetically affected resonances that are difficult to overcome. Although it has long been recognized that 13C NMR spectroscopy is likely to be a powerful complementary technique to overcome some of these limitations, the low sensitivity and low natural abundance of 13C nuclei has resulted in a lag in the application of 13C NMR spectroscopy to the study of paramagnetic hemes and heme proteins. The tremendous advances in methodology and instrumentation witnessed in the NMR field, coupled to the advent of recombinant DNA methods that have made possible the preparation and purification of significant quantities of proteins, and the biosynthesis of 13C-labeled heme, have contributed to an increased interest in the study of paramagnetic heme active sites by 13C NMR spectroscopy. As a consequence, 13C NMR spectroscopy is emerging as a powerful tool to study heme electronic structure and structure-function relationships in heme-containing proteins. In this report we strive to summarize some of the recent developments in the analysis of paramagnetic hemes and heme-containing proteins by 13C NMR spectroscopy.

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Structural, Magnetic, and Dynamic Characterization of the (d_xz,d_y_z)⁴(d_x_y)¹ Ground-State Low-Spin Iron(III) Tetraphenylporphyrinate Complex [(p-TTP)Fe(2,6-XylylNC)₂]CF₃SO₃

Cited by 86 publications

References 89 publications

Electronic ground states of low-spin iron(III) porphyrinoids

Electronic ground states of low-spin iron(III) porphyrinoids

Pulsed EPR and NMR Spectroscopy of Paramagnetic Iron Porphyrinates and Related Iron Macrocycles: How To Understand Patterns of Spin Delocalization and Recognize Macrocycle Radicals

Recent developments in the 13 C NMR spectroscopic analysis of paramagnetic hemes and heme proteins

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