The active sites of a representative non-heme iron hydroxylase, VioC (PDBID: 6ALM) and its vanadyl mimic (PDBID: 6ALR), were extracted from crystal structures of the enzyme. The native active site model comprised the Fe metal center, aKG, two metal-bound His ligands and one metal-bound Glu ligand truncated at the sidechain, i.e., excluding Ca and backbone atoms (Supporting Information Figure ). The active site model of the vanadyl mimic was mostly comparable to the native active site model except for an oxo moiety in the axial position and a succinate ligand in place of aKG (Supporting Information Figure ). Hydrogen atoms were then added to the extracted active sites using Avogadro v1.2.0 103 (Supporting Information Figure ). The metal-distal carboxylate oxygen atoms of aKG and succinate and the Nd atoms of His ligands were also protonated, resulting in active site models with a neutral charge (Supporting Information Figure ). All the heavy atoms in the final active site models were held fixed, and the added hydrogen atoms were optimized with UFF 104 . The isomers of the active sites containing water, O2, oxo, hydroxo, and monodentate as well as bidentate succinate ligands were generated with molSimplify 105 , which uses OpenBabel 106,107 as a backend. The crystal structures were used as starting points to generate additional intermediates: the vanadium or iron center was replaced by the other metal (i.e., Fe in place of V for oxo and hydroxo, V in place of Fe for water and O2) to generate the remaining initial geometries.