For the isomer shift, a motion with a high correlation coefficient (R 2 > 0.9) was obtained. The fit parameters and nuclear movements are similar at all temperatures (see SI, Figure ). For the quadrupole splitting, the R 2 value is lower (0.6183 to 0.6758) and the coefficients for each normal coordinate vary more strongly for the different see Figure . The resulting movement is overall similar at all temperatures. It comprises a strong out-of-plane movement of the iron ion combined with a substantial stretching of the axial iron-nitrogen bond and a weaker stretching of the in-plane iron-nitrogen bonds, as shown in Figure . This fits the expectations: the charge distribution in the out-of-plane direction changes strongly with this movement, thus converting the shape of the charge distribution from an oblate to a prolate shape and vice versa, which hence results in the observed sign swap of the quadrupole splitting. The differences in the calculated nuclear movements for different temperatures lie mostly in the motion of the in-plane nitrogen atoms. Their motion is more difficult to capture due to the asymmetry around the iron nucleus introduced by the 2-MeIm ligand and its CH 3 group close to the FeN 4 centre combined with the strong symmetry dependence of the quadrupole splitting.