Density functional theory (DFT) calculations for molecular models were performed using the ORCA program suite with the unrestricted Kohn-Sham formalism (UKS). The size variations of a 2+ charged model A and a neutral model B were investigated using ORCA 4.2 . Calculations on models without axial ligand containing 36 (A) and 52 (B) carbon atoms (system size 4) were rerun for a thorough spin state investigation with ORCA 5.0. 61,62 ORCA 5.0 was also used for the size variation of models with axial ligands. All calculations used "tight" SCF convergence criteria in ORCA nomenclature, the SMD solvent model with water and the split-RI-J approximation (for generalized gradient approximation (GGA) and meta-GGA functionals) or the RIJCOSXapproximation (hybrid functionals) with the auxiliary basis set def2/J 65 . ORCA 5.0 calculations used the predefined integration grid "DefGrid2". ORCA 4.2 calculations used an angular grid of size 6, with an increased grid size of 7 and an intacc setting of 7.0 for the iron atom in single point and Mössbauer calculations.