The Mössbauer parameters of the three models were predicted according to a previous calibration study. Whether the predicted differences are significant is judged with respect to the trust regions from calibration against experimental lowtemperature Mössbauer data (± 0.13 mm s -1 for the isomer shift and ± 0.36/0.22 mm s -1 for the quadrupole splitting, with ORCA 4.0/5.0 respectively, see also section 2). The predicted quadrupole splitting in Fe(II) square planar cases is highly sensitive to the specific electronic configurations converged by the DFT calculation of the numerous low-lying configurations; 29 a full treatment of the electronic structure is only possible via multideterminant methods. We note that recent work by some of us showed that the origins of the temperature dependence of the quadrupole splitting are rooted in small distortions around the iron ion due to vibrational effects, including zero-point vibrations. Including these effects can improve the agreement with experiment considerably, even if the electronic structure is retained. Herein, we cover these effects by relying on the uncertainty estimates from the calibration studies quoted above. The predicted differences in the isomer shifts of 0.548 mm s -1 (1), 0.621 mm s -1 (2) and 0.312 mm s -1 (3) are indicative of non-negligible differences in electron density at the iron nucleus for 1 and 2 vs. 3 (see Table for all Mössbauer parameters). The predicted quadrupole splitting values fall in a more narrow range: 1.878 mm s -1 (1), 1.354 mm s -1 (2) and 1.149 mm s -1 (3).