XAS STUDIES OF CPD I INTERMEDIATES

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We have collected Fe K-Edge XAS spectra for 11 ferric porphyrin compounds and the cpd I model [FeIV=O(TMP*)]+ in order to relate the intensity and multiplet splitting pattern of the 1s->3d pre-edge region to the geometric and electronic structure of the iron site. The ferric porphyrins studied fall into four categories: (1) 6-coordinate (low-spin) S=1/2; (2) 5-coordinate (high-spin) S=5/2; (3) 5-coordinate (spin admixed) S=5/2-3/2; (4) 6- coordinate (spin admixed) S=5/2-3/2. Our results conclusively show that the integrated intensity of the observed pre-edge features is diagnostic of these four classes. A detailed multiplet analysis of the 6-coordinate, low-spin complex [FeTMBPP]Cl has allowed for an experimental determination of the one-electron Fe ligand field state energies. To our knowledge, this represents the first direct measurement of the ligand field parameters for a ferric porphyrin. Interestingly, the information content of the pre-edge region is complementary to that obtainable by EPR spectroscopy. Extension of these methodologies should allow for detailed geometric and electronic structural information to be obtained on EPR silent ferrous porphyrins.