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. Author manuscript; available in PMC: 2007 Jan 10.
Published in final edited form as: Inorg Chem. 2004 May 3;43(9):2932–2942. doi: 10.1021/ic035119y

Variable π-Bonding in Iron(II) Porphyrinates with Nitrite, CO and tert-Butyl Isocyanide. Characterization of [Fe(TpivPP)(NO2)(CO)]−

Habib Nasri †, Mary K Ellison ‡, Maoyu Shang ‡, Charles E Schulz §,✉, W Robert Scheidt ‡,✉
PMCID: PMC1764913  NIHMSID: NIHMS11991  PMID: 15106981

Abstract

The addition of the strongly π-bonding ligands CO or tert-butyl isocyanide to the low-spin five-coordinate iron(II) nitrite species, [Fe(TpivPP)(NO2)]−, (TpivPP = picket fence porphyrin) gives two new six-coordinate species [Fe(TpivPP)(NO2)(CO)]− and [Fe(TpivPP)-(NO2)(t-BuNC)]−. These species have been characterized by single-crystal structure determinations and by UV-vis, IR and Mössbauer spectroscopies. All evidence shows that in the mixed-ligand iron(II) porphyrin species, [Fe(TpivPP)(NO2)(CO)]−, the two trans, π-accepting ligands CO and nitrite compete for π density. The CO ligand however dominates the bonding. The Fe–N(NO2) bond lengths for the two independent anions in the unit cell at 2.006(4) and 2.009(4) Å are lengthened compared to other nitrite species with either no trans ligands or non-π-accepting trans ligands to nitrite. The Fe–C(CO) bond lengths are 1.782(4) Å and 1.789(5) Å for the two anions. The two Fe–C–O angles at 175.5(4)° and 177.5(4)° are essentially linear in both anions. The quadrupole splitting for [Fe(TpivPP)(NO2)(CO)]− was determined to be 0.32 mm/s and the isomer shift was 0.18 mm/s at room temperature in zero applied field. Both of the Mössbauer parameters are much smaller than those found for six-coordinate low-spin iron(II) porphyrinates with neutral nitrogen-donating ligands as well as iron(II) nitro complexes. However, the Mössbauer parameters are typical of other six-coordinate CO porphyrinates signifying that CO is the more dominant ligand. The CO stretching frequency of 1974 cm−1 is shifted only slightly to higher energy compared to six-coordinate CO complexes with neutral nitrogen-donor ligands trans to CO. Crystal data for [K(222)][Fe(TpivPP)(NO2)− (CO)]·1/2C6H5Cl: monoclinic, space group P21/c, Z = 8, a = 33.548(6) Å, b = 18.8172(15) Å, c = 27.187(2) Å, β = 95.240(7)°, V = 17091(4) Å3.

Introduction

The binding of the diatomic molecules O2, CO, and NO to heme proteins is extremely important to mammalian physiology, while the binding of nitric oxide (NO), nitrite (NO2−) and nitrate (NO3−) to hemes is involved in important denitrification processes. Hence, the study of the bonding interaction between these biologically significant small molecules and others to hemes has been and continues to be an active area of research.1–3 However, despite great advances in understanding the many biological functions of these molecules, there remains considerable controversy about the mechanisms and identities of possible intermediates involved in their numerous reactions. For instance, the discrimination in binding of O2 over CO to hemes in respiration is not completely understood.4, 5 In addition, it is proposed that many of the intermediates in the inorganic nitrogen cycle involve the interaction of hemes with small nitrogen containing molecules; the exact identities of several are only speculative. In a recent mechanistic study6 of the reduction of nitrite to ammonia by cytochrome c nitrite reductase (ccNiR) it was proposed that the binding of nitrite to an iron(II) heme which starts the reaction cycle depends on the strong pi bond between nitrite and iron(II). The π bond leads to a strong Fe–N bond and a weakened N–O bond which can be cleaved heterolytically. Hence, the nature of the bond between nitrite and iron is critically important to the activation of this enzyme. Clearly, gaining insight into the bonding interaction between these small molecules and hemes through structural and physical studies is of interest.

Experimental Section

General Information

All manipulations for the preparation of the iron(II) six-coordinate porphyrin derivatives (see below), were carried out under argon using a double-manifold vacuum line, Schlenkware and cannula techniques. Chlorobenzene was purified by washing with concentrated sulfuric acid, then with water until the aqueous layer was neutral, then dried with MgSO4, and then distilled twice over P2O5.29 Hexanes were distilled from sodium/benzophenone. KNO2 was recrystallized twice from hot distilled water, dried overnight at about 75°C and stored under argon. Kryptofix-222 (Aldrich) was recrystallized from benzene (distilled from sodium/benzo-phenone) and stored under argon in the dark. The free base, (H2TpivPP), and the corresponding iron(III) chloro and triflato derivatives were synthesized by literature methods.30,31 UV-vis spectra were recorded on a Perkin-Elmer Lambda 19 UV/vis/near-IR spectrometer and IR spectra were recorded on a Perkin-Elmer Paragon 10000 FT-IR spectrometer as KBr pellets. Mössbauer measurements were performed on a constant acceleration spectrometer from 4.2 K to 300 K with optional small field and in a 9 T superconducting magnet system (Knox College). A sample of [K(222)][Fe(TpivPP)(NO2)(CO)]·1/2C6H5Cl for Mössbauer spectroscopy was prepared by immobilization of the crystalline material (crystals not ground but washed with water under argon) in Apiezon M grease.

Synthesis of [K(222)][Fe(TpivPP)(NO2)(CO)]·1/2C6H5Cl

[Fe(TpivPP)(SO3CF3)-(H2O)] (20 mg, 0.016 mmol) and ~1 mL of zinc amalgam in 8 mL of chlorobenzene were stirred for about 1 hour under argon. The deep red solution of [Fe(TpivPP)] was filtered into a second solution prepared by stirring (overnight) 80 mg of Kryptofix-222 (0.2 mmol) and 185 mg of KNO2 (2.2 mmol) in 7 mL of chlorobenzene. A stream of CO gas was passed (for about 15 min) through the dark red-yellow solution of the five-coordinate (nitro)iron(II) species, [Fe(TpivPP)(NO2)]−.20 The color changes slightly to light red as a result of forming the six-coordinate product [Fe(TpivPP)(NO2)(CO)]−. Single crystals of this complex were prepared by slow diffusion of hexanes into the chlorobenzene solution. UV-vis in C6H5Cl: λmax, nm (log ε); 414 (sh) (4.67); 434 (5.30); 546 (3.98). IR (KBr): ν(CO) 1974 (m) cm−1; ν(NO2−) 1383

Results

Reaction of the five-coordinate iron(II) species, [Fe(TpivPP)(NO2)]−, with CO or tert-butyl isocyanide gives the new anionic, six-coordinate iron(II) complexes [Fe(TpivPP)(NO2)(CO)]− and [Fe(TpivPP)(NO2)(t-BuNC)]−. Care must be taken to eliminate halide impurities that are known to coordinate strongly to iron(II) species. Hence, chlorobenzene was washed with concentrated sulfuric acid and Kryptofix-222 and KNO2 were recrystallized. The two six-coordinate species were characterized in solution with UV-visible spectroscopy using a specialized inert-atmosphere cell with 1 and 10-mm path lengths. Crystalline anionic iron porphyrinates were obtained as potassium-(Kryptofix-222) salts. Both species were characterized by infrared spectroscopy. The carbonyl stretching frequency for [Fe(TpivPP)(NO2)(CO)]− appears at 1974 cm−1. The C–N stretch is at 2101 cm−1 for [Fe(TpivPP)(NO2)(t-BuNC)]−. The solid-state Mössbauer quadrupole splitting, ΔEQ, for [K(222)][Fe(TpivPP)(NO2)(CO)]·1/2C6H5Cl was found to be 0.32 mm/s and the isomer shift, δ, was 0.18 mm/s at room temperature in zero applied field.

Discussion

Over the past several years, we have synthesized a number of (nitro)iron(II) porphyrin species. The successful syntheses of these complexes results from the strategic use of picket fence porphyrin and cryptate (or macrocyclic crown ether) cations. The five-coordinate anionic iron(II) nitrite species, [Fe(TpivPP)(NO2)]−, is prepared by addition of cryptand-solubilized KNO2 to the highly air-sensitive four-coordinate species [Fe(TpivPP)]. All of the characterized six-coordinate (nitro)iron(II) species result from the anaerobic addition of gaseous NO or CO or by addition of excess neutral ligand such as pyridine, pentamethylene sulfide, or t-butyl iso-cyanide to [Fe(TpivPP)(NO2)]− in solution. As shown by electronic spectroscopy, all of these six-coordinate species persist in solution under anaerobic conditions. In fact, the spectroscopic characterization of [Fe(TpivPP)(NO2)]− and the resulting six-coordinate species [Fe(TpivPP)-(NO2)(L)]− was our first indication that nitrite is a very unusual ligand. We begin our discussion with the effects of the ligands NO2− and CO on the electronic spectrum.

The electronic spectrum of [Fe(TpivPP)(NO2)]− has a Soret band at 444 nm. As can be seen from the electronic spectral data summarized in Table 2, this 444 nm Soret band for low-spin five-coordinate [Fe(TpivPP)(NO2)]− is strongly red-shifted compared to all of the other five- or six-coordinate iron(nitro) species thus far characterized. It is also strongly red-shifted compared to the spectrum of five-coordinate [Fe(TPP)(CO)]. The addition of a neutral ligand such as PMS or pyridine to [Fe(TpivPP)(NO2)]− causes the Soret band to blue shift by more than 10 nm. A similar blue shift in the Soret occurs upon addition of NO to the five-coordinate nitrite species. The Soret band at 407 nm for the low-spin, five-coordinate species [Fe(TpivPP)(NO)] is very blue shifted compared to [Fe(TpivPP)(NO2)]−. So what shift in the position of the Soret band should one expect when CO is added trans to nitrite? Probably the most well-known porphyrin CO-related spectroscopic change occurs when CO is added to five-coordinate high-spin thiolate hemes. These are the P450-type porphyrin derivatives, so-called because of the intense red-shifted Soret band at ~450 nm. A small red shift is also seen when a CO ligand is added to the five-coordinate [Fe(TPP)(CO)] species to give [Fe(TPP)(CO)2].

Table 2.

Electronic Spectral Data for Selected Iron(II) and Iron(III) Tetraarylporphyrins a

λmax (nm)
Complex Soret region (log ε) α, β region (log ε) ref.
Five-Coordinate Iron(II)
[Fe(TPP)(NO)]b 406 (4.97) 475(sh) 538 (4.00) 604 (3.45) 36
[Fe(TpivPP)(NO)]c 407 (5.15) 477(sh) (4.35) 539 (4.12) 607 (3.62) 25
[Fe(TMP)(NO)]d 408 (4.96) 477(sh) 539 (3.04) 611 (3.84) 37
[Fe(TPP)(CO)]e 419 537 570 ~610 38
[Fe(TpivPP)(NO2)]− c 433(sh) (4.94) 444 (5.12) 543(sh) (3.89) 567 (4.02) 608 (3.59) 20,22
Six-Coordinate Iron(II) Nitro
[Fe(TpivPP)(NO2)(CO)]−c 414 (sh) (4.67) 434 (5.30) 546 (3.98) tw
[Fe(TpivPP)(NO2)(t-BuNC)]−c 441 (5.52) 541 (4.20) 572 (3.45) tw
[Fe(TpivPP)(NO2)(NO)]− c 433 (5.17) 543 (4.14) 21
[Fe(TpivPP)(NO2)(Py)]− c 413(sh) (4.83) 430 (5.23) 533 (4.21) 560(sh) (3.66) 653 (2.83) 22
[Fe(TpivPP)(NO2)(PMS)]− c 418(sh) (4.88) 432 (5.07) 537 (4.18) 558(sh) (3.81) 653 (3.12) 22
Six-Coordinate Iron(II) Other
[Fe(TPP)(1-MeIm)(NO)]b 415 (5.26) 460 (4.26) 545 (3.99) 580(sh) (3.78) 643 (3.05) 39
[Fe(TPP)(4-NMe2Py)(NO)]d 416 554 586 40
[Fe(TPP)(1-MeIm)(NO)]d 416 543 583 641 40
[Fe(TPP)(4-MePip)(NO)]d 417 463 554 591 40
[Fe(TPP)(1-VinIm)2]d 424 (5.22) 533 (4.24) 564 (3.67) 41
[Fe(TPP)(1-BzlIm)2]d 426 (5.23) 533 (4.24) 565 (3.63) 41
[Fe(TPP)(1-AcIm)2]d 422 (5.14) 533 (3.99) 563 (3.62) 41
[Fe(TPP)(1-MeIm)2]d 425 (5.09) 533 (4.26) 564 (3.75) 41
[Fe(TpivPP)(1-MeIm)2]c 430 536 42
[Fe(TpivPP)(1-MeIm)2]e 432 (5.36) 537 (4.32) 562(sh) 43
[Fe(TpivPP)(Im−)(HIm)]−c 442 (4.00) 544 (3.47) 44
[Fe(TPP)(1-MeIm)(CO)]e 427 (5.50) 542 (3.95) 43
[Fe(TPP)(1-MeIm)(CO)]d 422 544 45
[Fe(TpivPP)(1-MeIm)(CO)]c 425 542 42
[Fe(TPP)(CO)2]e 426 551 578 38
Iron(II) Thiolates
[Fe(TpivPP)(SEt)]−c 421 533 575 625 46
[Fe(TpivPP)(SEt)(CO)]−c 392,467 565 612 46
[Fe(TpivPP)(SPh)]−c 421 536 575 625 46
[Fe(TpivPP)(SPh)(CO)]−c 403,464 555 605 46
Six-Coordinate Iron(III) Nitro
[Fe(TpivPP)(NO2)2]− c 364(sh) 426 (5.11) 464(sh) 553 (4.15) 23
[Fe(TpivPP)(NO2)(Py)]c 422 (5.26) 459 (sh) 550 (4.11) 24
[Fe(TPP)(NO2)(NO)]b 433 (5.34) 510(sh) (3.70) 545 (4.20) 577(sh) (3.70) 47
[Fe(Tp-OCH3PP)(NO2)(NO)]c 437 549 586 26
[Fe(TpivPP)(NO2)(NO)]e 433 543 581 26
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a

All spectra were taken at 25°C.

b

Chloroform solution.

c

Chlorobenzene solution.

d

Dichloromethane solution.

e

Toluene solution.

The average equatorial Fe–Np bond length for [Fe(TpivPP)(NO2)(CO)]−(1) is 1.992(7) Å and for [Fe(TpivPP)(NO2)(CO)]−(2) is 1.997(6) Å. These average bond lengths are the same as those found for the six-coordinate nitro species [Fe(TpivPP)(NO2)(PMS)]−,22 [Fe(TpivPP)-(NO2)(Py)]−,22 and [Fe(TpivPP)(NO2)(NO)]−.21 The average distance for these six-coordinate species is 0.02 Å longer than in the five-coordinate nitro species, [Fe(TpivPP)(NO2)]−. It is also slightly shorter (by 0.01 Å) than the Fe–Np bond length average of other CO complexes (confer Table 3).

Table 3.

Bond Distances (Å) for (Nitro)iron Porphyrin Derivatives

Iron(II) Complex Fe–Np Fe–N NO2 Fe–L ref.
[Fe(TpivPP)(NO2)(CO)]−(1) 1.992 (7) 2.006 (4) 1.782 (4) twa
[Fe(TpivPP)(NO2)(CO)] − (2) 1.997 (6) 2.009 (4) 1.789 (5) tw
[Fe(TpivPP)(NO2)] − 1.970 (4) 1.849 (6) 20,22
[Fe(TpivPP)(NO2)(PMS)] − 1.990 (6) 1.937 (3) 2.380 (2) 22
[Fe(TpivPP)(NO2)(Py)] − 1.990 (15) 1.951 (5) 2.032 (5) 22
[Fe(TpivPP)(NO2)(NO)] −b 1.988 (6) 2.086 (8) 1.792 (8) 21
[Fe(TpivPP)(NO2)(NO)] −c 1.986 (6) 2.060 (7) 1.840 (6) 21
Iron(III) Complex
[Fe(TpivPP)(NO2)(HIm)] 1.974 (2) 1.949 (10) 2.037 (10) 24
[Fe(TpivPP)(NO2)(Py)] 1.985 (3) 1.960 (5) 2.093 (5) 24
[Fe(TpivPP)(NO2)2] − 1.992 (1) 1.970 (5) 2.001 (6) 23
[Fe(TpivPP)(NO2)(SC6HF4)] − 1.980 (7) 1.990 (7) 2.277 (2) 25
[Fe(TpivPP)(NO2)(NO)]d 2.000 (5) 2.002 (2) 1.668 (2) 26
[Fe(TpivPP)(NO2)(NO)]e 1.996 (4) 1.998 (2) 1.671 (2) 26
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a

This work.

b

⊥ form.

c

|| form.

d

C2/c form.

e

P21/n form.

The iron–axial ligand bond lengths are sensitive to bonding changes and the largest structural changes occur upon coordination of a sixth ligand. The Fe–N(NO2) bond lengths for [Fe(TpivPP)(NO2)(CO)]−(1) and [Fe(TpivPP)(NO2)(CO)]−(2) are 2.006(4) Å and 2.009(4) Å, respectively. These are 0.16 Å longer than the Fe–N(NO2) bond length

Supplementary Material

SItables

Figure 1.

Figure 1

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ORTEP diagram of [Fe(TpivPP)(NO2)(CO)]−(1) showing the coordination at iron. 50% probability ellipsoids are depicted.

Figure 2.

Figure 2

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ORTEP diagram of [Fe(TpivPP)(NO2)(CO)]−(2). 50% probability ellipsoids are depicted. The rotational disorder in the nitro group and the pivalamide groups are shown.

Figure 3.

Figure 3

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ORTEP diagram of [Fe(TpivPP)(NO2)(CO)]−(1) looking down on the porphyrin plane.

Figure 4.

Figure 4

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ORTEP diagram of [Fe(TpivPP)(NO2)(CO)]−(2) looking down on the porphyrin plane.

Figure 5.

Figure 5

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Formal diagrams of the porphyrinato cores of [Fe(TpivPP)(NO2)(CO)]−(1) (top) and [Fe(TpivPP)(NO2)(CO)]−(2) (bottom). Illustrated are the displacements of each atom from the mean plane of the 24-atom porphyrin cores in units of 0.01 Å. Positive values of displacement are toward the NO2 ligand in each anion. The major orientation (54%) of the nitrite in anion 2 is the horizontal orientation. The diagram also gives the averaged values of each distinct bond distance and angle in the porphyrinato cores.

Figure 6.

Figure 6

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UV-vis spectra of [Fe(TpivPP)(NO2)]−, [Fe(TpivPP)(NO2)(CO)]−, and [Fe-(TpivPP)(NO2)(t-BuNC)]− taken under argon in chlorobenzene.

Figure S1.

Figure S1

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ORTEP diagram of the K(222) cryptand, cation 1.

Figure S2.

Figure S2

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ORTEP diagram of the K(222) cryptand, cation 2.

Figure S3.

Figure S3

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ORTEP diagram of [Fe(TpivPP)(NO2)(CO)]−(1) showing the coordination at iron. 50% probability ellipsoids are depicted and all atomic label are given.

Figure S4.

Figure S4

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ORTEP diagram of [Fe(TpivPP)(NO2)(CO)]−(2). 50% probability ellipsoids are depicted. The rotational disorder in the nitro group and the pivalamide groups are shown.

Figure S5.

Figure S5

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ORTEP of [Fe(TpivPP)(NO2)(CO)]−(1) looking down on the porphyrin plane.

Figure S6.

Figure S6

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ORTEP of [Fe(TpivPP)(NO2)(CO)]−(2) looking down on the porphyrin plane.

Table 1.

Crystallographic details for [K(222)][Fe(TpivPP)(NO2)(CO)]·1/2C6H5Cl

formula C89H105ClFeKN11O13
FW 1667.24
a, Å 33.548(6)
b, Å 18.8172(15)
c, Å 27.187(2)
β, deg 95.240(7)
V , Å3 17091(4)
Z 8
space group P21/c
Dc, g/cm3 1.296
F(000) 7056
μ, mm−1 0.325
crystal dimens, mm 0.24 × 0.12 × 0.08
absorption correction DIFABS
λ, Å 0.71073
T, K 130(2)
total data colld 52417
unique data 32440 (Rint = 0.0759)
unique obsd data [I > 2 σ(I)] 21632
refinement method on F2 (SHELXL)
final R indices [I > 2 σ(I)] R1 = 0.0775, wR2 = 0.1850
final R indices [for all data] R1 = 0.1224, wR2 = 0.2200
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Table 4.

Bond Parameters for (Carbonmonoxy)iron Porphyrin Derivatives

Complex Fe–Npa Fe–C(CO)a Fe–La Fe–C–Ob C–Oa ref.
[Fe(TpivPP)(NO2)(CO)]− (1) 1.992 (7) 1.782 (4) 2.006 (4) 175.5 (4) 1.150 (5) twc
[Fe(TpivPP)(NO2)(CO)] − (2) 1.997 (6) 1.789 (5) 2.009 (4) 177.5 (4) 1.140 (5) tw
[Fe(TPP)(Py)(CO)] 2.02 (3) 1.77 (2) 2.10 (1) 179 (2) 1.12 (2) 10
[Fe(Deut)(THF)(CO)] 1.98 (3) 1.706 (5) 2.127 (4) 178.3 (14) 1.144 (5) 13
[Fe(TPP)(SEt)(CO)] 1.993 (4) 1.78 (1) 2.352 (2) NR 1.17 (1) 14
[Fe(TPP)(1-MeIm)(CO)] 1.999 (7) 1.756 (2) 2.059 (1) 178.91 (17) 1.147 (2) d
2.003 (5) 1.793 (3) 2.071 (2) 179.3 (3) 1.061 (3) 11
[Fe(OEP)(1-MeIm)(CO)] 2.000 (3) 1.744 (5) 2.077 (3) 175.1 (4) 1.158 (5) 12
[Fe(TPpiv2C12P)(1-MeIm)(CO)] 1.999 (3) 1.728 (6) 2.062 (5) ~180 1.149 (6) 15
[Fe(β-PocpivP)(1,2-Me2Im)(CO)] 1.973 (8) 1.768 (7) 2.079 (5) 172.5 (6) 1.148 (7) 16
[Fe(C2-Cap)(1-MeIm)(CO)] 1.990 (7) 1.742 (7) 2.043 (6) 172.9 (6) 1.161 (8) 17
1.988 (13) 1.748 (7) 2.041 (5) 175.9 (6) 1.158 (8) 17
[Fe(OC3OPor)(1-MeIm)(CO)] 1.996 (12) 1.748 (7) 2.027 (5) 173.9 (9) 1.171 (8) 18
[Fe(OC3OPor)(1,2-Me2Im)(CO)] 2.00 (2) 1.713 (8) 2.102 (6) 180e 1.161 (10) 18
[Fe(C3-Cap)(1-MeIm)(CO)] 1.99 (2) 1.800 (13) 2.046 (10) 178.0 (13) 1.107 (13) 19
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a

Value in Å

b

Value in degrees.

c

This work.

d

An, J.; Beatty, A.; Scheidt, W. R., unpublished result.

e

Required by symmetry.

Table 5.

Solid-State Mössbauer Parameters for [Fe(TpivPP)(NO2)(CO)]− and Related Complexes

ΔEQ, mm/s δFe, mm/s T, K ref
[Fe(TpivPP)(NO2)(CO)]− 0.32 0.18 293 twa
0.28 0.28 15 tw
Iron(II) Complexes
[Fe(TMP)(Py)2] 1.24 0.45 4.2 58
[Fe(TPP)(Py)2] 1.15 0.40 77 59
[Fe(OEP)(Py)2] 1.13 0.46 4.2 60
[Fe(TPP)(1-VinIm)2] 1.00 0.43 4.2 41
[Fe(TPP)(Pip)2] 1.44 0.51 4.2 61
[Fe(TpivPP)(1-MeIm)2] 1.02 0.46 4.2 61
[Fe(TMP)(1-MeIm)2]b 1.11 0.45 77 62
[Fe(OEP)(1-MeIm)2]b 0.96 0.46 77 62
[Fe(TMP)(PMe3)(1-MeIm)]b 0.75 0.38 77 62
[Fe(TMP)(PMe3)2]b 0.47 0.36 77 62
[Fe(OEP)(PMe3)2]b 0.35 0.36 77 62
Iron(II) CO and CS Complexes
[Fe(TPP)(1-MeIm)(CO)] 0.35 0.20 293 63
[Fe(TPP)(Py)(CO)] 0.57 0.28 293 63
[Fe(Tp-OCH3PP)(Py)(CO)] 0.49 0.19 298 64
[Fe(Tp-OCH3PP)(HIm)(CO)] 0.36 0.18 298 64
[Fe(TpivPP)(1-MeIm)(CO)] 0.27 0.27 4.2 30
MbCO 0.35 0.27 4.2 65
[Fe(OEP)(4-CNPy)(CS)] 0.80 0.19 4.2 66
[Fe(OEP)(Py)(CS)] 0.57 0.15 4.2 66
[Fe(OEP)(Pip)(CS)] 0.65 0.19 4.2 66
[Fe(OEP)(4-NMe2Py)(CS)] 0.44 0.19 4.2 66
[Fe(OEP)(1-MeIm)(CS)] 0.42 0.14 4.2 66
Iron(II) Nitro Complexes
[Fe(TpivPP)(NO2)]− 2.28 0.41 4.2 22
[Fe(TpivPP)(NO2)(PMS)]− 1.18 0.42 4.2 22
[Fe(TpivPP)(NO2)(Py)]− 0.93 0.41 4.2 22
{FeNO}7 Complexes
[Fe(TpivPP)(NO2)(NO)]−c 1.78 0.22 200 21
[Fe(TpivPP)(NO2)(NO)]−d 1.20 0.35 4.2 21
[Fe(TPP)(NO)] 1.24 0.35 4.2 21
[Fe(OEP)(NO)] 1.26 0.35 100 67
[Fe(Deut)(NO)] 1.47 0.39 4.2 68
[Fe(TPP)(1-MeIm)(NO)] 0.73 0.35 4.2 40
[Fe(TPP)(4-MePip)(NO)] 0.91 0.37 4.2 40
Iron(III) Nitro Complexes
[Fe(TpivPP)(NO2)2]− 2.1 0.25 4.2 24
[Fe(TpivPP)(NO2)(Py)] 2.2 0.26 4.2 24
[Fe(TpivPP)(NO2)(SC6HF4)]− 2.12 0.22 293 25
2.30 0.28 4.2 25
{FeNO}6 Complexes
[Fe(OEP)(Iz)(NO)]+ 1.99 −0.07 293 69
1.92 0.02 4.2 69
[Fe(OEP)(2-MeHIm)(NO)]+ 1.88 0.05 4.2 70
[Fe(OEP)(1-MeIm)(NO)]+ b 1.64 0.02 4.2 71
[Fe(OEP)(NO)]ClO4 1.55 0.13 293 69
1.64 0.20 4.2 69
[Fe(Tp-OCH3PP)(NO2)(NO)] 1.43 0.04 293 26
[Fe(TpivPP)(NO2)(NO)] 1.48 0.01 293 26
1.43 0.09 4.2 26
[Fe(TPP)(NO2)(NO)] 1.37 0.02 293 26
1.36 0.13 4.2 26
1.36 0.13 77 72
[Fe(OEP)(C6H4-p-F)(NO)] 0.56 0.05 293 73
0.57 0.14 4.2 73
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a

This work.

b

In dimethylacetamide solution.

c

form.

d

|| form.

Acknowledgments

We thank the National Institutes of Health for support of this research under Grant GM-38401. Funds for the purchase of the FAST area detector diffractometer were provided through NIH Grant RR-06709 to the University of Notre Dame.

Footnotes

Contribution from The Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, Faculté des Sciences de Monastir, Avenue de l’environnement, 5019 Monastir, Tunisia and Department of Physics, Knox College, Galesburg, Illinois 61401

Supporting Information Available: Tables S1–S6, giving complete crystallographic details, atomic coordinates, bond distances and angles, anisotropic temperature factors, and fixed hydrogen atom positions for [K(222)][Fe(TpivPP)(NO2)(CO)]·1/2C6H5Cl and Figures of K(222) cations and complete labelled diagrams of the [Fe(TpivPP)(NO2)(CO)]− anions. (PDF). An X-ray crystallographic file, in CIF format, is available. This material is available free of charge via the Internet at http://pubs.acs.org.

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SItables
NIHMS11991-supplement-SItables.doc (216.5KB, doc)

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