Molecular structure of the chloroiron(III) derivative of the meso-unsubstituted 2,7,12,17-tetramethyl-3,8,13,18-tetramesitylporphyrin and weak ferromagnetic exchange interactions in the A1u oxoiron(IV) porphyrin π radical cation complex

Khadija Ayougou, Dominique Mandon, Jean Fischer, Raymond Weiss, Markus Müther, Volker Schünemann, Alfred X. Trautwein, Eckhard Bill, James Terner, Karupiah Jayaraj, A. Gold, Rachel N. Austin

22 Citations (Scopus)

Abstract

The molecular structure of the chloroiron(III) porphyrinate [Fe IIICl(tmtmp)] (1) is described. The doming of the bifacially encumbered tmtmp dianionic ligand present in 1 is characterized by a separation of 0.09(1) Å between the mean plane of the four pyrrole nitrogens (4N p) and that of the porphyrin core. The coordination polyhedron of the five-coordinate iron atom is a square pyramid of C4v symmetry. The metal is displaced by 0.44(1) Å from the 4Np mean plane towards the axial chloro ligand. The Fe-Np and Fe-Cl bond lengths are 2.057(6) and 2.223 (5) Å, respectively. Upon treatment of [Fe IIITf(tmtmp)] (2) with m-chloroperoxybenzoic acid, the green oxoferryl π radical cation complex [FeIV=O(tmtmp)]+ (3) is obtained. It has been studied by EPR, Mössbauer, and resonance Raman spectroscopy. It exhibits an EPR spectrum strikingly similar to those of compounds I of Micrococcus lysodeikticus catalase (MLC-I) and ascorbate peroxidase (APX-I). The exchange interactions between the spins of the radical cation and the ferryl iron are of the ferromagnetic type and are the weakest ever found for a synthetic compound I model. The shift of + 22 cm-1 in the radical marker band ν2 in the resonance Raman spectra upon oxidation of 2 to 3 confirms that the electronic state of the porphyrin π radical cation is predominantly 2A1u in this tmtmp compound I model.

Original languageEnglish
JournalChemistry - A European Journal
Volume2
Issue number9
Pages (from-to)1159-1163
Number of pages5
ISSN0947-6539
DOIs
Publication statusPublished - 01.12.1996

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