Magnetic Interactions in the High-Spin Iron(III) Oxooctaethylchlorinato Derivative [Fe(oxoOEC)(Cl)] and Its π-Cation Radical [Fe(oxoOEC•)(Cl)]SbCl6

The preparation and characterization of the β-oxochlorin derivative [3,3,7,8,12,13,17,18-octaethyl-(3H)-porphin-2-onato(2−)]iron(III) chloride, [Fe(oxoOEC)(Cl)], and its π-cation radical derivative [Fe(oxoOEC•)(Cl)]SbCl6 is described. Both compounds have been characterized by single-crystal X-ray structure determinations, IR, UV/vis/near-IR, and Mössbauer spectroscopies, and temperature-dependent magnetic susceptibility measurements. The macrocycles of [Fe(oxoOEC)(Cl)] and [Fe(oxoOEC•)(Cl)]SbCl6 are both saddled, and [Fe(oxoOEC•)(Cl)]SbCl6 is slightly ruffled as well. [Fe(oxoOEC)(Cl)] shows a laterally shifted dimeric unit in the solid state, with a mean plane separation of 3.39 Å and a lateral shift of 7.39 Å. Crystal data for [Fe(oxoOEC)(Cl)]: triclinic, space group P1̄, Z = 2, a = 9.174(2) Å, b = 13.522(3) Å, c = 14.838(3) Å, α = 95.79(3)°, β = 101.46(2)°, γ = 104.84(3)°. Upon oxidation, the inter-ring geometric parameters increase; the mean plane separation and the lateral shift of the dimeric unit of [Fe(oxoOEC•)(Cl)]SbCl6 are 4.82 and 8.79 Å, respectively. Crystal data for [Fe(oxoOEC•)(Cl)]SbCl6: monoclinic, space group Cc, Z = 4, a = 19.8419(13) Å, b = 10.027(2) Å, c = 22.417(4) Å, β = 96.13(2)°. A broad near-IR absorption band appears at 1415 nm for the π-cation radical, [Fe(oxoOEC•)(Cl)]SbCl6. Zero-field Mössbauer measurements at 4.2 K for both [Fe(oxoOEC)(Cl)] and [Fe(oxoOEC•)(Cl)]SbCl6 confirmed that the oxidation state of the iron atom did not change upon chemical oxidation. Solid-state magnetic susceptibility measurements for [Fe(oxoOEC•)(Cl)]SbCl6 resulted in a large temperature dependence of the magnetic moment that can best be fit with a model that includes a zero-field splitting parameter of D = 6 cm-1, antiferromagnetic intermolecular iron−iron coupling (2J Fe - Fe = −0.14 cm-1), antiferromagnetic intramolecular iron−radical coupling (2J Fe - r = −76 cm-1), and antiferromagnetic radical−radical coupling (2J r - r = −13 cm-1).