Investigating superoxide transfer through a μ-1,2-O₂ bridge between nonheme Ni^III-peroxo and Mn^II species by DFT methods to bridge theoretical and experimental views

Previously, a fast unprecedented O₂^•- transfer reaction has been observed experimentally when adding a Mn^II complex into a solution containing a Ni^III-peroxo complex. Due to the fast reaction rate, no intermediates were observed. We have investigated this reaction with density functional theory (DFT) and show that DFT is unusually problematic in reproducing the correct spin state for the investigated Ni ^III-peroxo complex, something which calls for examination of all previous Ni-dioxygen studies. Surprisingly, the BP86 functional is shown to yield energies more in agreement with known experiments than B3LYP. The calculations reveal for the first time an intermediate structure in a complete O₂^•- transfer reaction, shown here to be a short-lived bridging Ni-(μ-1,2-O₂)-Mn structure.