Elucidating the Correlation between the Redox Potential, Spin State and Crystal Structure in a Series of Ferrous Complexes with Redox‐Active Ligands

Accurately predicting the spin crossover (SCO) temperature (T1/2) in spin crossover compounds remains a significant challenge, due to their extreme sensitivity to minor variations in ligand and crystal structure. In this study, we uncover a critical link between the redox potential of ligands and SCO behavior within Hofmann‐type clathrates {Fe(R‐pbpy+)2[µ2‐M(CN)4]2} (R = electron‐donating or electron‐withdrawing groups, M = Pd or Pt). Through precise tuning of the ligands' electronic properties, we establish a correlation between redox potential, space group, and SCO temperature, explained by an adaptation of Marcus theory of electron transfer. These findings not only provide a deeper understanding of the factors governing SCO behavior but also present a promising strategy for the rational design of SCO materials with tailored properties.