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. Author manuscript; available in PMC: 2006 Sep 5.
Published in final edited form as: Acta Crystallogr Sect E Struct Rep Online. 2006 Aug;62(8):m1892–m1894.

Bis (pyridine) (2,3,12,13-tetrabromo-5, 10, 15, 20-tetraphenylporphyrin) iron (II) pyridine solvate

W Robert Scheidt 1, Bruce C Noll 1
PMCID: PMC1560092  NIHMSID: NIHMS11330  PMID: 16957782

Abstract

The title compound, (C44H24Br4N4)(C5H5N)2Fe·C5H5N, is located on a two-fold axis that passes through Fe and the pyridine ligands. Only slight asymmetry, 0.010 Å elongation due to the Br substituents, is seen in the Fe–Np distances. The pyridine ligands are twisted 19.2° from each other.

Comment

The title compound [Fe(TPPBr4)(py)2] is a low-spin bis(pyridine)iron(II) complex that was studied as part of a program of ways to achieve control of axial ligand orientation in iron porphyrin derivatives (Safo et al., 1991). Two effects are possible with this porphyrin ligand: the effect from the four β-pyrrole electron-withdrawing substituents and the possible conformation effects of the peripherally crowded but asymmetrically substituted porphyrin.

The molecular structure of the title compound is shown in Fig. 1. The core asymmetry is very small with Fe—Np bond distances of 1.971 (2) and 1.981 (2) Å, with only a very small elongation caused by the bromo substituents. This is very much less than some derivatives, for example two different crystalline forms of high-spin [Fe(TPPBr4)]2O (Kadish et al., 1997; Li et al., 2000) have Fe—Np bond distances that differ by greater than 0.05 Å. A similar, even larger difference is seen in [Zn(TPPBr4)] (Zou et al., 1997). However, small differences (1.90 and 1.91 Å) are also seen in [Ni(TPPBr4)] (Zou et al., 1994) and in two crystalline forms of [Fe(TPPBr4)(NO)] (Scheidt et al., 2000) suggesting that the magnitude of the asymmetry in the porphyrin hole size is related to the natural bond lengths and strength of the bonds. The average 1.976 (7) Å bond length is at the very low end of distances observed for low-spin iron(II) (Scheidt, 2000). The small size of the central hole is the result, at least in part, of the core conformation in [Fe(TPPBr4)(py)2]. The core is substantially distorted from planarity by a combination of both ruffling and saddling. The deformation shows asymmetry because of the two types of pyrrole rings leading to overall core symmetry of C2 and not S4. Unlike the case of [Fe(TFPPBr8)(py)2] where the strongly saddled core led to a near perpendicular orientation of the two axial pyridine ligand planes (Grinstaff et al., 1995), the core appears to have had little effect on the orientation of the two pyridine planes; the angle between the two pyridines is 19.18 (13)°. It has been previously noted that coplanar axial ligands are typically seen in iron(II) porphyrin systems (Safo et al., 1997). The axial Fe—Npy bond distances of 2.000 (3) and 2.040 (3) Å are within the normal range observed.

Fig. 1.

Fig. 1

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Thermal ellipsoid plot of Fe(TPPBr4)(py)2. Ellipsoids drawn at 50% probability. Unique part of molecule drawn with solid bonds. H atoms and solvent omitted for clarity. Symmetry code: (i) −x, y, −z+1 1/2.

Examination of crystal packing (Fig. 2) shows the pyridine to be in a channel perpendicular to (001). The porphyrins pack in pairs of chains also perpendicular to (001) and alternating concave up and concave down along a chain.

Fig. 2.

Fig. 2

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View of crystal packing perpendicular to (001).

Experimental

The β-pyrrole substituted tetrabromotetraphenylporphyrin derivative (H2TPPBr4) was synthesized following the reported method (Callot, 1974). The perchlorato- and chloroiron(III) derivatives were prepared by modified literature methods (Alder et al., 1970; Buchler, 1975; Dolphin et al., 1977). The bispyridine ligated iron complex was prepared by stirring the perchlorate derivative with pyridine under argon for 1 h. Single crystals were obtained by liquid diffusion of hexane into a CH2Cl2 solution. The crystals grown exhibited iron in +2 oxidation state (UV-vis λmax= 436, 540, 576 nm).

Crystal data
C54H34Br4FeN6.C5H5N Mo Kα radiation
Mr = 1221.46 λ = 0.71073 Å
Monoclinic Cell parameters from 8017 reflections
C2/c θ = 2.55–28.5°
a = 18.4633 (5) Å μ = 3.658 mm−1
b = 19.9786 (6) Å T = 100 (2) K
c = 14.4636 (4) Å Block
β = 114.688 (1)° Dark red
V = 4847.5 (2) Å3 0.15 × 0.11 × 0.11 mm
Z = 4 Crystal source: synthesized
Dx = 1.674 Mg m−3
Dm not measured
Data collection
Bruker x8–ApexII CCD diffractometer 4952 reflections with >2sigma(I)
ϕ and ω scans
Absorption correction: Rint = 0.0391
 multi-scan SADABS, Sheldrick (2004) θmax = 28.55°
 Please give reference h = −24 → 24
 Tmin = 0.60, Tmax = 0.67 k = −26 → 26
51139 measured reflections l = −19 → 19
6171 independent reflections every 0. reflections
frequency: 0. min
Refinement
Refinement on F2 w=1/[σ2(Fo2) + (0.0578P)2 + 9.6451P]
R[F2 > 2σ(F2)] = 0.0365 where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.1082 (Δ/σ)max = 0.001
S = 1.095 Δρmax = 1.032 e Å−3
6171 reflections Δρmin = −1.020 e Å−3
323 parameters Extinction correction: none
H-atom parameters constrained Scattering factors from International Tables for Crystallography (Vol. C)
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The molecule of pyridine cocrystallized with the porphyrin is about an inversion center at (0, 1/2, 1/2). The N position in this pyridine solvate could not be determined due to the crystallographically imposed disorder. Thus, all pyridine atoms were refined as C and the three associated H atoms were included at 0.8333 occupancy. All H atoms were refined using a riding model with C—H distances equal to 0.95%A and Uiso equal to 1.2(UisoC).

Data collection: APEX2 (Bruker–Nonius AXS, 2004). Cell refinement: APEX2/SAINT (Bruker–Nonius AXS, 2004). Data reduction: SAINT/XPREP (Bruker–Nonius AXS, 2004; Sheldrick, 2003). Program(s) used to solve structure: SHELXS-97 (Sheldrick, 2001). Program(s) used to refine structure: SHELXL97 (Sheldrick, 2001). Molecular graphics: XP (Sheldrick, 1998). Software used to prepare material for publication: XCIF (Sheldrick, 2001)/enCIFer (CCDC, 2004).

Acknowledgments

The authors thank the US NIH, grant GM-38401, and NSF, grant CHE-0443233, for support.

Footnotes

Supplementary data for this paper are available from the IUCr electronic archives (Reference: PREVIEW). Services for accessing these data are described at the back of the journal.

References

  1. Alder AD, Longo FR, Kampus F, Kim J. JINCS. 1970;32:2443. [Google Scholar]
  2. Bruker-Nonius AXS. (2004). APEX2 and SAINT Bruker-Nonius AXS, Madison, Wisconsin, USA.
  3. Buchler, J. W. (1975). Porphyrins and Metalloporphyrins. Smith, K. M., Ed. Amsterdam, The Netherlands: Elsevier Scientific Publishing. ch., 5.
  4. Callot, H. J. (1974). Bull. Soc. Chim. Fr. 1492.
  5. CCDC. (2004). enCIFer The Cambridge Crystallographic Data Centre, Cambridge, UK.
  6. Dolphin D, Sams JR, Tsin TB. Inorg Chem. 1977;16:711. [Google Scholar]
  7. Grinstaff MW, Hill MG, Birnbaum ER, Schaefer WP, Labinger JA, Gray HB. Inorg Chem. 1995;34:4896–4902. [Google Scholar]
  8. Kadish KM, Autret M, Ou Z, Tagliatesta P, Boschi T, Fares V. Inorg Chem. 1997;36:204–207. [Google Scholar]
  9. Li M, Shang M, Duval HF, Scheidt WR. Acta Cryst C. 2000;56:1206–1207. doi: 10.1107/s0108270100010222. [DOI] [PubMed] [Google Scholar]
  10. Safo MK, Gupta GP, Walker FA, Scheidt WR. J Am Chem Soc. 1991;113:5497–5510. [Google Scholar]
  11. Safo MK, Nesset MJM, Walker FA, Debrunner PG, Scheidt WR. J Am Chem Soc. 1997;119:9438–9448. [Google Scholar]
  12. Scheidt, W. R. (2000). The Porphyrin Handbook. Kadish, K. M., Smith, K., Guilard, R., Editors. San Diego, CA and Burlington, MA: Academic Press. Volume 3, ch. 16.
  13. Scheidt WR, Duval HF, Neal TJ, Ellison MK. J Am Chem Soc. 2000;122:4651–4659. [Google Scholar]
  14. Sheldrick, G. M. (1998). XP Bruker-Nonius AXS, Madison, Wisconsin, USA.
  15. Sheldrick, G. M. (2001). XCIF, XL, and XS. Bruker-Nonius AXS, Madison, Wisconsin, USA.
  16. Sheldrick, G. M. (2003). XPREP Bruker-Nonius AXS, Madison, Wisconsin, USA.
  17. Sheldrick, G. M. (2004). SADABS Universität Göttingen, Germany.
  18. Zou J, Li M, Xu Z, You X. Acta Chim Sinica. 1994;52:683–692. [Google Scholar]
  19. Zou JZ, Li M, Xu Z, You XZ. Jiegou Huaxue (Chinese J Struct Chem) 1997;16:2931. [Google Scholar]

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