During spin-state switching in SCO complexes, a significant distortion from ideal octahedral geometry in the SCO metal center was observed, where the LS state represents a more regular structure than the HS state. Several octahedral distortion parameters 105 (, , ) can be used to determine the extent of such distortions around the iron(II) center (Table ). For complex 1 at 280 K, distortion parameters ,  and  are 125.0°, 334.2°and 0.578 Å, respectively, which lie in the expected range observed for the HS iron(II) complex. Upon lowering the temperature to 110 K, these values decrease significantly to 78.1°, 201.3°and 0.565 Å, respectively, which are expected to lie in the range of the distortion parameters for the LS iron(II) complex. The structural distortion of the iron(II) center was also evaluated using CShM using the SHAPE program (Tables and), where a zero value of the shape factor implies an ideal octahedral geometry. The outcome from the CShM analyses is consistent with the above-stated observations. the SCO unit and associated counter anion play a significant role in determining the spin-state switching behavior. There are significant CH- interactions among the isopropyl CH-and the phenyl ring of BPh4 -counter anion, - interactions present between the pyridine ring from the macrocyclic ligand and the phenyl ring of BPh4 ¯ counter anion present in the system (Figure )