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. 2010 Sep 6;49(17):8078-85.
doi: 10.1021/ic101099z.

Structural and magnetic effects of meso-substitution in alkyl-substituted metalloporphyrinate pi-cation radicals: characterization of [Fe(TalkylP*)(Cl)]SbCl6 (alkyl = ethyl and n-propyl)

Ming Li  1 , Teresa J Neal, Graeme R A Wyllie, Charles E Schulz, W Robert Scheidt
Affiliations

Structural and magnetic effects of meso-substitution in alkyl-substituted metalloporphyrinate pi-cation radicals: characterization of [Fe(TalkylP*)(Cl)]SbCl6 (alkyl = ethyl and n-propyl)

Ming Li et al. Inorg Chem. .

Abstract

We report the preparation and characterization of two meso-alkyl substituted porphyrin pi-cation radical derivatives, [Fe(TalkylP(*))(Cl)]SbCl(6) (alkyl = ethyl or propyl). Both complexes have been characterized by UV/vis/near-IR, IR, and Mossbauer spectroscopy, temperature-dependent solid-state magnetic susceptibility measurements, and X-ray structure determinations. All data for both oxidized species are consistent with the formulation of the complexes as ring-oxidized iron(III) porphyrin species. The molecular structures of the two five-coordinate species have the typical square-pyramidal coordination group of high-spin iron(III) derivatives. The crystal structures also reveal that the species form cofacial pi-pi dimers with lateral shifts of 1.44 A and 3.22 A, respectively, for the propyl and ethyl radical derivatives. Both radicals exhibit porphyrin cores with alternating bond distance patterns in the inner 16-membered ring. In addition, [Fe(TEtP(*))(Cl)]SbCl(6) and [Fe(TPrP(*))(Cl)]SbCl(6) have been characterized by temperature-dependent (6-300 K) magnetic susceptibility studies, the best fitting of the temperature-dependent moments reveal strong coupling between iron spins and porphyrin radical, and a smaller magnitude of antiferromagnetic coupling between ring radicals, which are opposite to those found in the five-coordinate iron(III) OEP radicals. The differences in structure and properties of the cation radical meso-alkyl and beta-alkyl derivatives possibly reflect differences in properties of a(1u)- and a(2u)-forming radicals.

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Figures

Figure 1
Figure 1
UV-vis spectra of [Fe(TEtP)(Cl)] (- - -) and [Fe(TEtP.)(Cl)]SbCl6 (—)(Top), and [Fe(TPrP)(Cl)] (- - -) and [Fe(TPrP.)(Cl)]SbCl6] (—) (Bottom) in CH2Cl2 solution. Insets in both sets of spectra display the near-IR band of [Fe(TEtP.)(Cl)]SbCl6 (top) and [Fe(TPrP.)(Cl)]SbCl6 (bottom).
Figure 2
Figure 2
ORTEP diagram of [Fe(TEtP.)(Cl)]SbCl6 displaying the atom labeling scheme. Thermal ellipsoids of all atoms are contoured at the 50% probability level. Hydrogen atoms have been omitted for clarity.
Figure 3
Figure 3
ORTEP diagram of [Fe(TPrP.)(Cl)]SbCl6 displaying the atom labeling scheme. Thermal ellipsoids of all atoms are contoured at the 50% probability level. Hydrogen atoms have been omitted for clarity.
Figure 4
Figure 4
Edge-views of the dimeric units of [Fe(TEtP.)(Cl)]+ (top) and [Fe(TPrP.)(Cl)]+ (bottom). 50% probability ellipsoids are shown. The scale of this figure and Figure 5 are identical.
Figure 5
Figure 5
Top-views of the dimeric units of [Fe(TEtP.)(Cl)]+ (top) and [Fe(TPrP.)(Cl)]+ (bottom). (50% probability ellipsoids).
Figure 6
Figure 6
Formal diagrams of the porphinato core displaying perpendicular displacements, in units of 0.01Å, of the core atoms from the 24-atom mean plane. Also entered on the diagrams are the values of the individual bond distances in the inner 16-membered rings. Note the alternating short-long pattern of the N–Ca and Ca–Cm bond distances. [Fe(TEtP.)(Cl)]SbCl6 (top), [Fe(TPrP.)(Cl)]SbCl6 (bottom).
Figure 7
Figure 7
Comparison of observed and calculated values of µeff/monomer vs T for [Fe-(TEtP.)(Cl)]SbCl6 (○) and [Fe(TPrP.)(Cl)]SbCl6] (▽). The lines (solid or dashed) are model calculations assuming pairwise spin coupling. The fit parameters used are given in Table 3. Also shown in the figure are the T-dependent magnetic susceptibilities for the precursors [Fe(TPrP)(Cl)] (●) and [Fe(TEtP)(Cl)] ((△) that have been described previously.
Scheme 1
Scheme 1
Plots of HOMOs of a1u and a2u symmetry. The magnitude of the orbital coefficients are depicted by the size of the circles with shaded/unshaded indicating the sign.
Scheme 2
Scheme 2
Diagram illustrating structural features found in cofacial porphyrin dimers. Quantities displayed include the mean plane separation, MPS, the center to center distance, Ct⋯Ct, and the lateral shift of the two ring centers, LS.
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References

    1. Abbreviations: TPP, dianion of tetraphenylporphyrin; OEP, dianion of octaethylporphyrin; OEC, dianion of octaethylchlorin; Ca, pyrrole α carbon pyrrole; Cb, β carbon; Cm, methine carbon atom; Np, porphinato nitrogen atom.

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