Electronic structures of group 9 metallocorroles with axial ammines

The electronic structures of metallocorroles (tpfc)M(NH₃) ₂ and (tfc)M(NH₃)₂ (tpfc is the trianion of 5,10,15-(tris)-pentafluorophenylcorrole, tfc is the trianion of 5,10,15-trifluorocorrole, and M = Co, Rh, Ir) have been computed using first principles quantum mechanics [B3LYP flavor of Density Functional Theory (DFT) with Poisson-Boltzmann continuum solvation]. The geometry was optimized for both the neutral systems (formal MIII oxidation state) and the one-electron oxidized systems (formally MVI). As expected, the MIII systems have a closed shell d6 configuration; for all three metals, the one-electron oxidation was calculated to occur from a ligand-based orbital (highest occupied molecular orbital (HOMO) of B₁ symmetry). The ground state of the formal MIV system has MIII-Cπ character, indicating that the metal remains d6, with the hole in the corrole π system. As a result the calculated MVI/III reduction potentials are quite similar (0.64,0.67, and 0.56 V vs SCE for M = Ir, Rh and Co, respectively), whereas the differences would have been large for purely metal-based oxidations. Vertically excited states with substantial metal character are well separated from the ground state in one-electron-oxidized cobalt (0.27 eV) and rhodium (0.24 eV) corroles, but become closer in energy in the iridium (0.15 eV) analogues. The exact splittings depend on the chosen functional and basis set combination and vary by∼0.1 eV.