[Raman and IR spectroscopic analysis of substituted tetraphenylporphyrin iron complexes]

In the present paper, two series of substituted tetraphenylporphyrin iron compounds RTPPFe(II) and RTPPFeCI (III) were synthesized by two-step synthetic method. Raman and IR spectra of tetraphenylporphyrin iron complexes were investigated. By analyzing the IR and Raman spectra of RTPPFe(II) and RTPPFe(III)Cl, it was confirmed that the RTPPFe(II) complexes were usually unstable at normal temperature and existed via the coordination of dioxygen with the iron (II) center, i.e. they formed into TPPFe-O2, and the stable configuration of dioxygen with the iron (II) center was "end-on". In addition, the geometric structure optimization of substituted iron tetraphenylporphyrin complexes was performed by PM3 semi-empirical and MM+ method quantum calculation. The structure parameters were obtained, including E(HOMO), E(LUMO) and total energy, bond length of Fe-Cl etc. The effect of molecular structure on vibrational frequency shift was studied by combing the IR and Raman spectra. The results showed that for iron tetraphenylporphyrins (RTPPFe-O2) with different structure, the vibrational frequencies of the Fe-O bond were associated with their twist degree of molecular structures, i.e. the Raman and IR characterization vibrational frequencies of the Fe-O2 were up shifted with the increase in the Fe-O-O angle of iron tetraphenylporphyrins (RTPPFe-O2) molecule.