Kinetics and mechanism of the reaction between the di-μ-cyanobis[tetracyanoferrate(III)] complex ion and sulfite in aqueous solution

The kinetics of the stepwise reduction of the title complex [Fe2(CN)10]4− by sulfite have been studied in the presence of air as a function of pH, sulfite concentration, temperature and ionic strength using stopped-flow and conventional spectrophotometric techniques. The k obs versus pH profile shows a marked increase in rate with increase of pH over the range 3.7 ⩽ pH ⩽ 6.1 due to the increase in concentration of the more reactive sulfite species View the MathML sourceSO32-. The reaction proceeds in several stages, the first of which involves a one electron transfer process with the formation of the radical anion View the MathML sourceSO3- This then adds on in a rapid stage to form a species View the MathML source[Fe2III(CN)10(SO3)]5-. The second and third stages also involve one electron transfer. In the third, or possibly a fourth stage cleavage occurs, the final product being [FeII(CN)5(SO3)]5−. The reaction rate is sensitive to the nature of the cation present with a reactivity sequence View the MathML sourceLi+