Overall, our findings show that the results from both molecular and periodic models are in good agreement with each other and experimental data. Besides designing a chemically meaningful structural model, future studies should ensure that a high quality of electronic structure description is used to avoid artefacts, e.g. GGA+U with a benchmarked value for U, or carefully chosen hybrid functionals. By leveraging the strengths of both molecular and periodic approaches, a comprehensive understanding of the energetics of possible spin states of iron and the corresponding Mössbauer parameters can be obtained. This information as well as other spectroscopic properties provide a direct point of comparison with experimental data on FeNC catalysts under ex situ, in situ and operando conditions.