The geometries of ferrous-dioxygen adducts, of their one-electron reduced counterparts, and
of the corresponding (protonated) ferric-hydroperoxide adducts, of heme models where the
axial ligand is thiolate, phenoxide, imidazole, imidazolate, or it is actually missing, were
optimized using the non-hybrid density functional theory. A detailed comparison of the bond
lengths, bond orders, partial atomic charges and molecular orbitals of these models
indicates anionic ligands such as thiolate to be only slightly better than neutral ligands at …