10.1021/ic201972f.s001 Hailiang Zhao Hailiang Zhao Kristine Pierloot Kristine Pierloot Ernie H. G. Langner Ernie H. G. Langner Jannie C. Swarts Jannie C. Swarts Jeanet Conradie Jeanet Conradie Abhik Ghosh Abhik Ghosh Low-Energy States of Manganese–Oxo Corrole and Corrolazine: Multiconfiguration Reference ab Initio Calculations American Chemical Society 2012 δ2 ground states ground states ab initio multiconfiguration reference methods ANO CASPT RASPT ground state 2012-04-02 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Low_Energy_States_of_Manganese_Oxo_Corrole_and_Corrolazine_Multiconfiguration_Reference_ab_Initio_Calculations/2535754 Manganese­(V)–oxo corrole and corrolazine have been studied with ab initio multiconfiguration reference methods (CASPT2 and RASPT2) and large atomic natural orbital (ANO) basis sets. The calculations confirm the expected singlet d<sub>δ</sub><sup>2</sup> ground states for both complexes and rule out excited states within 0.5 eV of the ground states. The lowest excited states are a pair of Mn­(V) triplet states with d<sub>δ</sub><sup>1</sup>d<sub>π</sub><sup>1</sup> configurations 0.5–0.75 eV above the ground state. Manganese­(IV)–oxo macrocycle radical states are much higher in energy, ≥1.0 eV relative to the ground state. The macrocyclic ligands in the ground states of the complexes are thus unambiguously ‘innocent’. The approximate similarity of the spin state energetics of the corrole and corrolazine complexes suggests that the latter macrocycle on its own does not afford any special stabilization for the Mn<sup>V</sup>O center. The remarkable stability of an Mn<sup>V</sup>O octaarylcorrolazine thus appears to be ascribable to the steric protection afforded by the β-aryl groups.