A key finding is that square-planar coordination environments cannot support an Fe(II) high spin configuration. Models of this type therefore cannot be used to explain the experimental observation of this type of Mössbauer signature. A chemically meaningful model with an Fe(II) high spin configuration requires for the iron atom to be lifted outside the plane of the equatorial carbon environment. This can be achieved in molecular tetracoordinate models by introducing defects that lead to a curved graphene environment. Differences between the spin state predictions of molecular and periodic models were traced back to structural differences, most importantly the enforced planarity of the periodic models. For a periodic model with an out-of-plane iron in a pyrrolic environment, a high spin configuration was found, albeit at slightly higher energy than the in-plane model. A similar type of curvature can be present in carbon nanotubes, which are best described with a periodic approach. Alternatively, axial ligands can be bound at iron, which also lift it from the graphene-based plane and alter the ligand field splitting such that high spin states become energetically accessible.