Following the protocol from prior work , initial geometries to generate isomerization reaction coordinates (RCs) were constructed from the PBE0/def2-TZVP optimized geometries of active site isomers by rotating oxo/hydroxo with respect to the axial His in 1° increments of the angle formed by the oxo, the metal center (i.e., Fe, V), and the nitrogen of the axial His (Supporting Information Figure ). Constraints were employed for each of the isomerization RCs and constrained optimizations were performed along the chosen RC for both iron and vanadium metal centers at the PBE0/def2-TZVP level of theory in ORCA v.4.0.1.2 (Supporting Information Table and Figure ). To understand the effect of different metal centers for a given geometry, singlepoint calculations were obtained on optimized geometries of Fe intermediates by replacing Fe with V and vice versa. High-energy structures along the RCs were used to obtain vibrational frequencies. Numerical Hessian calculations were carried out at the same level of theory, and the Hessian was computed using the central difference approach after 6N atomic displacements. The presence of an imaginary frequency along the RC confirmed that the high-energy structure corresponded to a transition state. Multiwfn 114 was used to perform Mayer bond order analysis in order to quantify the strength of binding of aKG, monodentate, and bidentate succinate to both iron and vanadium metal centers.