Chlorido(2,3,7,8,12,13,17,18-octaethylporphyrinato)iron(III): a new triclinic polymorph of Fe(OEP)Cl

The previous structure determination of the title compound, [Fe(C36H44N4)Cl], was of a monoclinic polymorph [Senge (2005). Acta Cryst. E61, m399-m400]. The crystal structure of a new triclinic polymorph has been determined based on single-crystal X-ray diffraction data collected at 100 K. The asymmetric unit contains one molecule of the high-spin square-pyramidal iron(III) porphyrinate. The structure exhibits distinct nonstatistical alternative positions for most atoms and was consequently modeled as a whole-molecule disorder. The compound is characterized by an average Fe-N bond length of 2.065 (2) angstrom, an Fe-Cl bond length of 2.225 (4) angstrom, and the iron(III) cation displaced by 0.494 (4) angstrom from the plane of the 24-atom porphyrinate core, essentially the same as in the previously determined polymorph. Common features of the porphyrin plane-plane stacking involve two types of synthons, each of which can be further stabilized with additional H center dot center dot center dot Cl interactions to the axial chloride ligand, exhibiting concerted interactions of H atoms from the ethyl groups with the pi-cloud electron density of adjacent molecules; the shortest methylene H-atom contacts are in the range 2.75-2.91 angstrom, resulting in plane-plane separations of 3.407 (4) and 3.416 (4) angstrom, and the shortest methyl H-atom contacts are 2.56-2.95 angstrom, resulting in plane-plane separations of 4.900 (5) and 4.909 (5) angstrom in the monoclinic polymorph. The plane-to-plane stacking synthons in the triclinic polymorph are similar, but at greater distances; the shortest methylene H-atom contacts are 2.86-2.94 angstrom, resulting in plane-plane separations of 3.45 (2) and 3.45 (3) angstrom, and the shortest methyl H-atom contacts are 2.89-3.20 angstrom, resulting in plane-plane separations of 5.081 (13) and 5.134 (13) angstrom, consistent with the density of the triclinic polymorph being 1.5% lower, suggesting lesser packing efficiency and lower stability in the triclinic polymorph. The major molecular differences found in the polymorphs is in three different orientations of the ethyl-group side chains on the periphery of the porphyrin core.