X-ray absorption spectroscopy of exemplary platinum porphyrin and corrole derivatives: metal- versus ligand-centered oxidation

A combination of Pt L(3)-edge X-ray absorption spectroscopy (EXAFS and XANES) and DFT (TPSS) calculations have been performed on powder samples of the archetypal platinum porphyrinoid complexes Pt(II)[TpCF(3)PP], Pt(IV)[TpCF(3)PP]Cl(2), and Pt(IV)[TpCF(3)PC](Ar)(py), where TpCF(3)PP(2−) = meso-tetrakis(p-trifluoromethylphenyl)porphyrinato and TpCF(3)PC(3−) = meso-tris(p-trifluoromethylphenyl)corrolato. The three complexes yielded Pt L(3)-edge energies of 11 566.0 eV, 11 567.2 eV, and 11 567.6 eV, respectively. The 1.2 eV blueshift from the Pt(ii) to the Pt(iv) porphyrin derivative is smaller than expected for a formal two-electron oxidation of the metal center. A rationale was provided by DFT-based Hirshfeld which showed that the porphyrin ligand in the Pt(iv) complex is actually substantially oxidized relative to that in the Pt(ii) complex. The much smaller blueshift of 0.4 eV, going from Pt(IV)[TpCF(3)PP]Cl(2), and Pt(IV)[TpCF(3)PC](Ar)(py), is ascribable to the significantly stronger ligand field in the latter compound.