Spectroscopic discernibility of dopants and axial ligands in pyridinic FeN₄ environments relevant to single-atom catalysts

Single-atom catalysts (SACs) activate small molecules, e.g. the oxygen reduction reaction is catalysed by FeNC materials. Because the nature of active site(s) in this type of SAC is unclear, spectroscopic and computational insights are needed to clarify the atomistic composition and electronic structure. Using quantum chemistry, we show that key features of [Fe{phen₂A₂}L]ⁿ⁺ complexes (A = CH, N with n = 0, A = O with n = 0, 2; L = OH⁻, Cl⁻) can be differentiated spectroscopically.