Fe L- and K-edge XAS of low-spin ferric corrole: bonding and reactivity relative to low-spin ferric porphyrin.
Corrole is a tetrapyrrolic macrocycle that has one carbon atom less than a porphyrin. The ring contraction reduces the symmetry from D(4h) to C(2v), changes the electronic structure of the heterocycle, and leads to a smaller central cavity with three protons rather than the two of a porphyrin. The differences between ferric corroles and porphyrins lead to a number of differences in reactivity including increased axial ligand lability and a tendency to form 5-coordinate complexes. The electronic structure origin of these differences has been difficult to study experimentally as the dominant porphyrin/corrole pi --> pi* transitions obscure the electronic transitions of the metal. Recently, we have developed a methodology that allows for the interpretation of the multiplet structure of Fe L-edges in terms of differential orbital covalency (i.e., the differences in mixing of the metal d orbitals with the ligand valence orbitals) using a valence bond configuration interaction model. Herein, we apply this methodology, combined with a ligand field analysis of the Fe K pre-edge to a low-spin ferric corrole, and compare it to a low-spin ferric porphyrin. The experimental results combined with DFT calculations show that the contracted corrole is both a stronger sigma donor and a very anisotropic pi donor. These differences decrease the bonding interactions with axial ligands and contribute to the increased axial ligand lability and reactivity of ferric corroles relative to ferric porphyrins.
Hocking
Rosalie K
RK
Department of Chemistry, Stanford University, Stanford, California 94305, USA.
DeBeer George
Serena
S
Gross
Zeev
Z
Walker
F Ann
FA
Hodgson
Keith O
KO
Hedman
Britt
B
Solomon
Edward I
EI
D004583:Electrons; D005290:Ferric Compounds / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D008956:Models, Chemical; D011166:Porphyrins / Q000737:chemistry; D056928:X-Ray Absorption Spectroscopy
D005290:Ferric Compounds; D008665:Metalloporphyrins; D011166:Porphyrins; C431863:corrole