Crystal structure of bis(1-methyl-1H-imidazole-κN 3)(5,10,15,20-tetraphenylporphyrinato-κ4 N)iron(II)–1-methyl-1H-imidazole (1/2)

The title compound, [Fe(C44H28N4)(C4H6N2)2]·2C4H6N2, is a six-coordinate FeII–porphyrinate complex with the metal located on a center of inversion and coordinated by two axial 1-methylimidazole ligands; the complex crystallizes as a 1-methylimidazole disolvate. The 1-methylimidazole group bonded to the FeII atom [occupancy ratio 0.789 (4):0.211 (4)] and the unbound 1-methylimidazole molecule [0.519 (4):0.481 (4)] were disordered. The average Fe—N(porphyrinate) bond length is 1.998 (3) Å and the axial Fe—N(imidazole) bond length is 1.9970 (12) Å. In the crystal, molecules are linked into a three-molecule aggregate by two weak C—H⋯N interactions.


Related literature
For the function and structure of bis-histidine-coordinated cytochromes b, see: Xia et al. (1997). For the structures of other models of bis-histidine-coordinated hemes in proteins, see: Walker (2004). For the parallel and perpendicular orientation preferences of imidazole ligands in model porphyrins, see: Safo et al. (1991). For the synthesis of some bis-imidazole complexes, see: Higgins et al. (1991). The structure of Fe(TPP)(1-MeIm) 2 (i.e. the solvate-free title compound) was briefly mentioned in a meeting abstract, but no structural information is available, see: Steffen et al. (1978). For an example of a complex with a low-spin ferrous center, see: Scheidt & Reed (1981 Table 1 Hydrogen-bond geometry (Å , ).

S1. Introduction
Bis-histidine coordinated hemes are present in a number of cytochrome b complexes, and are known to be involved in electron transfer processes (Xia et al., 1997). The parallel and perpendicular relative orientations of the histidine ligands are believed to have correlations with the spectroscopic properties of the proteins (Walker, 2004). As models of bishistidine coordinated cytochrome b, several cationic bis-imidazole coordinated porphyrin complexes have been synthesized and their structures have been determined . Here, we report the molecular structure of a neutral bis-imidazole coordinated Fe II complex, Fe(TPP)(1-MeIm) 2 . 2(1-MeIm). The molecular structure of the titled compound is shown in Fig. 1. The porphyrin complex was located on an inversion center. The 1-methylimidazole groups bonded to the metal and the unbound 1-methylimidazoles were disordered. The average Fe-Np bond distance is 1.998 (3) Å and the axial Fe-N Im distance is 1.9970 (12) Å, suggesting a low-spin ferrous center (Scheidt & Reed, 1981). The two 1-MeIm planes are mutually parallel. The projection of the axial ligand has a dihedral angle of 28.04 (15)° with the closest Fe-Np bond.

S2. Experimental
The Fe(TPP)(1-MeIm) 2 . 2(1-MeIm) was obtained serendipitously as follows: To a 10 ml CH 2 Cl 2 solution of (TPP)FeCl (0.010 g, 0.014 mmol) was added N-hydroxyamphetamine (7 mg, 46.3 mmol) and 1-MeIm (0.05 ml, 29.0 mmol) under nitrogen. The color of the solution changed from brown to reddish purple during a 6 h period. The solution was dried under reduced pressure. The residue was dissolved in CH 2 Cl 2 and filtered, and an equal volume of hexane was added. A red plate shaped crystal grew from the slow evaporation of this mixture at room temperature under nitrogen.

S3. Refinement
H atoms were located geometrically and treated as riding on their parent atoms with C-H = 0.95 Å for aromatic and 0.98 Å for aliphatic, with U iso (H) = 1.2-1.5U eq (C). The 1-methylimidazole groups bonded to the metal were disordered.
The occupancies of the metal bound ligands were refined to 0.789 (4) and 0.211 (4) for the unprimed and primed atoms.
The occupancies of the unbound imidazoles refined to 0.519 (4) and 0.481 (4) for the A and B molecules.

Figure 1
The molecular structure of the title compound showing atom-labeling scheme and displacement ellipsoids drawn at the 50% probability level. H atoms have been omitted for clarity.