In this work, our data set of mononuclear square pyramidal Fe and Ru catalysts consists of complexes both with monodentate ligands only and complexes with macrocyclic ligands. The complexes with monodentate ligands were inspired by prior work and comprise 70 homoleptic and heteroleptic structures in each spin state (i.e., LS, IS, and HS), resulting in 210 complexes for both Fe and Ru. These structures contain small, monodentate ligands from a set of ten ligands that span ligand field strengths and metal-coordinating atom identities (Figure ). The initial set of 70 structures comprise all 10 possible homoleptic complexes. The remaining 60 heteroleptic complexes randomly sample a space of 180 complexes that can be formed with combinations of two ligands out of our set of ten ligands. We consider two geometries where the equatorial plane is both symmetric, i.e., comprises four identical ligands with a different axial ligand, and cissymmetric, i.e., comprises two unique ligands each of which is cis to each other, with an axial ligand that is the same as one of the two unique equatorial ligands (Figure and Supporting Information Tables and). The complexes with macrocyclic ligands were directly adapted from separate prior work from which we only considered 543 Fe complexes from the initial set of catalysts for which the DFT geometry optimization of the Fe-oxo intermediate had successfully converged. The 543 Ru counterparts of these complexes were newly generated in the present work by a direct metal substitution. In these complexes, the equatorial positions are all occupied by a realistic tetradentate macrocyclic ligand constructed using known ligand fragments, and the axial position contains a monodentate ligand from the set of aniline, phenol, phenylphosphine, and thiophenol in both neutral and anionic forms that is coordinating to the metal via the 2p/3p atoms of the ligand (Figure and Supporting Information Figure ). Thus, in this work, a theoretical set of 1506 Fe or Ru catalysts was considered prior to elimination of failed calculations (see Sec. Ru) with monodentate ligands. The set of ten small, monodentate ligands used to construct these complexes are shown ordered based on increasing ligand field strength and each complex comprises up to two unique ligands. Complexes in this set can be homoleptic with five identical monodentate ligands, equatorially symmetric where the equatorial ligands are identical with a different axial ligand or equatorially cis-symmetric where the equatorial plane consists of two unique ligands that are each cis to each other and the axial ligand is identical to one of the equatorial ligands. (bottom) Structural configuration of the 1,086 square pyramidal complexes (543 Fe and 543 Ru) with a tetradentate macrocyclic ligand in the equatorial plane and a monodentate axial ligand. Three examples of tetradentate equatorial ligands and all eight axial ligands that are used to construct this set of complexes are shown with the metal-coordinating atom shaded in translucent green circles. Atom color codes: H in white, C in gray, N in blue, O in red, F in light blue, P in orange, S in yellow, and Cl in green.