Journal of Applied Sciences

Year: 2005 | Volume: 5 | Issue: 4 | Page No.: 773-780
DOI: 10.3923/jas.2005.773.780

Kinetics and Mechanism of the Oxidation of Dicyano-BIS-(2,2’-Bipyridine) Iron (II) Complex by Meta Periodate

Oladega O. Soriyan, Jide Ige, A.O. Fadiran and O. Owoyomi

Abstract: The reaction of Dicyano-bis-(2,2’-bipyridine) Iron (II) Trihydrate with periodate shows 1.5 order overall; first order with respect to the complex and half-order with respect to IO^-₄. A detailed mechanism involving a series of one-electron transfer steps is proposed and shows agreement with experimental data. The kinetics and mechanism of the reaction exhibit significant solvent medium dependence. The reaction shows complexities resulting from the variety of species of both reactants present in solution. This is reflected in the ionic strength dependence studies. In acid and hydroxyl ion medium, the reaction strength dependence in neutral (distilled water) medium, indicative of the charges on the reacting species in the different media. Slopes of log k_r vs I^1/2 are less than unity in all cases. The rate law in acid medium is The corresponding rate law in OH^- medium is Observed inhibition by H⁺ and OH^- is due to the less reactive HFe(bipy)₂(CN)⁺₂ and H₂Fe(bipy)₂(CN)⁺₂ species formed in H⁺ medium and dimeric H₂I₂O^4-₁₀ in OH^- medium. IO⁺₃ is suggested as one of the reactive periodate ions in acid medium. The reaction takes place through mixed inner and outer sphere mechanisms in acid and neutral medium. Electron transfer by the formation of an outer-sphere complex is the only possible reaction path in OH^- medium. Observed autocatalysis suggests the accumulation of reactive intermediate(s).