While changes in planarity thus have a quantifiable influence on the orbital composition, there is no direct correspondence with the change in Mössbauer parameters that goes beyond the more immediate influence of the local ligand field distortion: the iron ion sitting above the plane spanned by the four nitrogen atoms in 3 leads to a stabilisation and double occupation of the d z 2 orbital, hence a different electron density at the iron ion, resulting in a lowered isomer shift compared to 1 and 2. A pronounced, but less easily quantifiable effect than covalency stems from electronic effects due to defects, e.g. the number and position of the seven-membered rings. The inseparable dependence of geometry and electronic structure, the specific manifestation of an electronic structure in a given ligand field, and thereby its influence on spectroscopic discernibility and ultimately catalytic activity, can only be evaluated in concrete molecular models.