Magnetic interactions in the high-spin iron(III) oxooctaethylchlorinato derivative [Fe(oxoOEC)(Cl)] and its pi-cation radical [Fe(oxoOEC(center dot))(Cl)]SbCl6

The preparation and characterization of the beta-oxochlorin derivative [3,3 ,7,8,12,13,17,18-octaethyl-(3H)-porphin 2-onato(2-)]iron(III) chloride, [Fe (oxoOEC)(Cl)], and its pi-cation radical derivative [Fe(oxoOEC(.))(Cl)]SbCl 6 is described. Both compounds have been characterized by single-crystal X- ray structure determinations, IR, UV/vis/near-IR, and Mossbauer spectroscop ies, and temperature-dependent magnetic susceptibility measurements. The ma crocycles 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 pl ane separation of 3.39 A and a lateral shift of 7.39 Angstrom. Crystal data for [Fe(oxoOEC)(Cl)]: triclinic, space group (P) over bar 1, Z = 2, a = 9. 174(2) Angstrom, b = 13.522(3) Angstrom, C = 14.838(3) Angstrom, alpha = 95 .79(3)degrees, beta = 101.46(2)degrees, gamma 104.84(3)degrees Upon oxidati on, 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 A, respectively. Crystal data for [Fe(oxoOEC(.))(Cl)]SbCl6: m onoclinic, space group Cc, Z = 4, a = 19.8419(13) Angstrom, b = 10.027(2) A ngstrom, c = 22.417(4) Angstrom, beta = 96.13(2)degrees. A broad near-IR ab sorption band appears at 1415 nm for the rr-cation radical, [Fe(oxoOEC(.))( CI)]SbCl6. Zero-field Mossbauer: measurements at 4.2 K for both [Fe(oxoOEC) (Cl)] and [Fe(oxoOEC(.))(Cl)]SbCl6 confirmed that the oxidation state of th e iron atom did not change upon chemical oxidation. Solid-state magnetic su sceptibility measurements for [Fe(oxoOEC(.))(Cl)]SbCl6 resulted in a large temperature dependence of the magnetic moment that can best be fit with a m odel that includes a zero-field splitting parameter of D = 6 cm(-1) antifer romagnetic intermolecular;r 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)).