Quantifying the effect of high-spin/low-spin crossover on electron delocalization in d⁵d⁵ M₂Cl₉^3- (M = Fe, Ru, Os) dimers

Density functional theory has been used to investigate the effect of high-spin/low-spin crossover on the delocalization of metal-based electrons in homo- and hetero-bimetallic d⁵d⁵ face-shared M₂Cl₉^3- (M = Fe, Ru, Os) dimers. The energetic contributions of the ligand-field, ΔE_LF, spin-polarization, ΔE_spe, and orbital overlap, ΔE_ovlp, terms to the high-spin/low-spin and localized/delocalized equilibria in these dimer systems have been quantified. The two equilibria are found to exhibit a strong linear dependence, which can be attributed to their connection with the single-ion spin-polarization energy. It can be concluded that metal-metal bond formation necessitates a crossover from a high-spin to low-spin configuration in these dimer systems, and, therefore, neither delocalized high-spin or localized low-spin d⁵d⁵ structures are likely to occur.