To In order to understand the period dependence and coordination environment effects (2p, a combination of 2p and 3p, and 3p) on reaction energetics, we evaluate variations with dopant atoms for ΔE(oxo) and ΔE(HAT) of Fe and Ru codoped SACs with the same coordination environment (Figure ). Overall, the 3p (i.e., P or S) dopants in codoped SACs make ΔE(HAT) more favorable but ΔE(oxo) less favorable relative to 2p elements (i.e., N or O) in codoped SACs (Supporting Information Figure ). This trend holds for Ru or Fe but is subtler than the earlier observation that ΔE(oxo) energetics on Fe codoped SACs are less favorable than Ru codoped SACs while ΔE(HAT) energetics on Ru codoped SACs are less favorable than Fe SACs (Supporting Information Figure ). For the outliers to these general observations, e.g., LS 6-membered Ru(III)(6-8 N4-S2) SACs versus LS 6-membered Fe(III)(6-8 N4-S2) SACs, we identify that the inclusion of S dopants in the second coordination sphere induces distinct graphene flake distortion for Fe vs. Ru (Figure ). This distortion occurs in opposing directions between the LS 6-membered Ru(III)(6-8 N4-S2) SACs and the LS 6-membered Fe(III)(6-8 N4-S2) SACs. The trend in increasing HAT favorability for 3p dopants is similar to those that have been previously observed for Fe(II) complexes for methane-to-methanol conversion 101 . Nevertheless, in other cases, the origin appears more electronic in nature, such as a 6-membered Fe(II)(N1O3) SAC where oxo formation is more favorable for Fe(II) than Ru(II), despite a weaker ligand field (Figure ). Overall, both electronic and structural differences in 2p and 3p dopants play a role in relative energetics of SAC catalysts, but the metal dependence (i.e., 3d vs 4d) is stronger than the dependence on coordination environment (i.e., 2p vs 3p).