The quadrupole splitting is defined by the electric field gradient at the iron nucleus and mainly controlled by the symmetry of the electric field. Increasing the number of carbon atoms has a minimal effect on the symmetry of the FeN 4 center. This is true even for 2, where the carbon environment is more planar in the extended model, but the local coordination environment of the nitrogen atoms changes only slightly. The significant effect on the quadrupole splitting in 1 may be in part due to known uncertainties when predicting electronic structures of square-planar complexes with DFT as a singledeterminant method, and can be explained in part by a change in d xz /d yz orbital occupation and the different admixture of ligand character (see Table for more information on the orbital occupations).