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

Abstract

A combination of Pt L₃-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[TpCF₃PP], Pt^IV[TpCF₃PP]Cl₂, and Pt^IV[TpCF₃PC](Ar)(py), where TpCF₃PP²⁻ = meso-tetrakis(p-trifluoromethylphenyl)porphyrinato and TpCF₃PC³⁻ = meso-tris(p-trifluoromethylphenyl)corrolato. The three complexes yielded Pt L₃-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[TpCF₃PP]Cl₂, and Pt^IV[TpCF₃PC](Ar)(py), is ascribable to the significantly stronger ligand field in the latter compound.