SPIN COUPLING IN DISTORTED HIGH-VALENT FE(IV) PORPHYRIN RADICAL COMPLEXES

In order to study structural influences on the interaction of Fe(IV) ( S = 1) and porphyrin cation radical (S' = 1/2) in high-valent iron por phyrin complexes of the type \X-(TMP)Fe=O\(+)(Cl-), X=I, Br-2,Br-4 wer e generated by mCPBA oxidation of corresponding Fe(III) porphyrins. Th e halogen substitution at the peripheral positions of the porphyrin le ads to distortion of the planar porphyrin ring of \(TMP)Fe=O\(+). The new species have beeen investigated by temperature-dependent EPR and f ield-dependent Mossbauer spectroscopy; for the evaluation of spectra, we adopted the spin-Hamiltonian formalism including exchange interacti on explicitly. As in \(TMP)Fe=O\(+), strong ferromagnetic spin couplin g was observed with \J(0)\/D=0.9-1 and a zero-field spitting of D simi lar to 32 cm(-1). For consistent parametrization of EPR and Mossbauer results, anisotropic coupling had to be introduced. Compared to \(TMP) Fe=O\(+)[1], analysis of the spectroscopic data shows that zero-field splitting and spin coupling is only slightly affected by the halogen d istortion of the porphyrin structure.