Role of the Imide Axial Ligand in the Spin and Oxidation State of Manganese Corrole and Corrolazine Complexes.

Electronic structure calculations have been performed on four different Mn corrole and corrolazine complexes to clarify the role of the imide axial ligand on the relative stability of the different spin states and the stabilization of the high-valent Mn ion in these complexes. Multiconfigurational perturbation theory energy calculations on the DFT-optimized geometries show that all complexes have a singlet ground state except the complex with the strongest electron-withdrawing substituent on the imide axial ligand, which is found to have a triplet ground state. The analysis of the σ and π interaction between the metal and imide ligand shows that this spin crossover is caused by a subtle interplay of geometrical factors (Mn-N distance and coordination angle) and the electron-withdrawing character of the substituent on the imide, which reduces the electron donation to the metal center. The analysis of the multiconfigurational wave functions reveals that the formally Mn(V) ion is stabilized by an important electron transfer from both the equatorial corrole/corrolazine ligand and the axial imide. The macrocycle donates roughly half an electron, being somewhere between the closed-shell trianionic and the dianionic radical form. The imide ligand transfers 2.5 electrons to the metal center, resulting in an effective d-electron count close to five in all complexes.