Mössbauer investigations of the hexachlorantimonate salt of the phenyliron 2,3,7,8,l2,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrinate, [Fe(oetpp)Ph]SbCl6 and X-ray structure of the phenyliron(III) precursor Fe(III)(oetpp)Ph

Abstract

The phenyliron derivative, [Fe(oetpp)C6H5)]SbCl6 (2) generated in dichloromethane by oxidation of the phenyliron(III) complex, Fe(III) (oetpp)C6H5 (1) of the 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin with 1 equiv. of phenoxathiinylium hexachloroantimonate, [C12H8OS]SbCl6, was studied by Mössbauer spectroscopy. This compound exhibits an isomer shift δ of 0.13 mm s−1 and a quadrupole splitting ΔEQ of 3.23 mm s−1. The measured magnetic hyperfine pattern obtained in the temperature range 4.2–40 K in a field of 3.5 and 7 T, applied perpendicular to the γ-beam, has been consistently analyzed in the spin Hamiltonian approximation assuming an iron(IV) S=1 electronic configuration. This result indicates that oxidation of the ferric precursor 1 causes oxidation of the metal and not from the macrocycle. This finding corresponds to that of the corrole complex Fe(me2et6c)C6H5 (me2et6c=trianion of 7,13-dimethyl-2,3,8,l2,l7,l8-hexaethylcorrole) which recently was also characterized as an iron(IV) S=1 derivative. The molecular structure of the five-coordinate, low-spin, ferric starting derivative, Fe(oetpp)C6H5 (1) is reported. A comparison of the porphyrin ring conformations in the phenyliron(III) species, Fe(tpp)C6H5 (3) and Fe(oetpp)C6H5 (1) indicates that the more favorable oxidation potential of the oetpp complex 1 relative to that of the non-peripherally crowded tpp ring derivative 3 is related to the non-planar distortion of the oetpp ring, distortion which is, due to the steric crowding, maintained in solution.