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

Abstract

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) Å, an Fe—Cl bond length of 2.225 (4) Å, and the iron(III) cation displaced by 0.494 (4) Å 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...Cl interactions to the axial chloride ligand, exhibiting concerted interactions of H atoms from the ethyl groups with the π-cloud electron density of adjacent molecules; the shortest methylene H-atom contacts are in the range 2.75–2.91 Å, resulting in plane–plane separations of 3.407 (4) and 3.416 (4) Å, and the shortest methyl H-atom contacts are 2.56–2.95 Å, resulting in plane–plane separations of 4.900 (5) and 4.909 (5) Å 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 Å, resulting in plane–plane separations of 3.45 (2) and 3.45 (3) Å, and the shortest methyl H-atom contacts are 2.89–3.20 Å, resulting in plane–plane separations of 5.081 (13) and 5.134 (13) Å, 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.