Mechanism of the molecular hysteresis

The redox behavior in acetone solution of (1,5‐dithiacyclooctane 1‐oxide)bis(pentaammineruthenium(II)) has been characterized, where the concept of “molecular hysteresis” is presented. Detailed thermodynamics for the complex are studied, in which intramolecular electron transfer rates for Ru3+OS/Ru2+→Ru2+SO/Ru3+ were determined as 0.12 sec−1 and 0.055 sec−1. The molecular hysteresis consists of two important factors: isomerizations for the sulfoxideruthenium complexes and the slow intramolecular electron transfer in the complex; both are examined. Isomerization rates for Ru3+S→O and Ru2+O→S determined range from 0.4 to 5000 sec−1 and from 0.7 to 16 sec−1, respectively, for [Ru(NH3)5(sulfoxide)]2+/3+. A mechanism for the slow electron transfer in the complex is also presented. Features of molecular hysteresis are discussed.