Binding one or two axial ligands alters the ligand field splitting, so that the spin ground state can change and thus lead to different Mössbauer parameters. To evaluate whether the different models would lead to different Mössbauer signals during the oxygen reduction reaction, as detected in ex situ, in situ and operando experiments, models with one or two representative axial ligands (O 2 , OH -, H 2 O) were constructed . All plausible overall multiplicities were evaluated, see Tables and for the relative energies and electronic structure information.