Electron Transfer Reaction of Tris(1,10-phenanthroline)cobalt(III) Complex and Iodide Ion in An Aqueous Acidic Medium
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ORIGINAL ARTICLE
Electron Transfer Reaction of Tris(1,10‑phenanthroline)cobalt(III) Complex and Iodide Ion in An Aqueous Acidic Medium D. E. Arthur1 · I. U. Nkole2 · C. R. Osunkwo2 Received: 19 July 2020 / Accepted: 4 November 2020 © The Tunisian Chemical Society and Springer Nature Switzerland AG 2020
Abstract The kinetics and mechanistic study of the electron transfer of tris(1,10-phenanthroline)cobalt(III) complex and iodide ion has been carried out in an aqueous acidic medium at ionic strength(I) = 0.20 mol dm−3 (NaCl), [ H+] = 0.02 mol dm−3, T = 28 ± 1.0 °C and λmax of 495 nm. The rate of reaction was found to be third order overall: first order in the oxidant and second order in the reductant, and acid independent. The empirical rate law conforms to the equation:
− = k[(Co(phen)3 )3+ ][I− ]2 The reaction rate was unaffected by change in ionic strength and dielectric constant of the reaction medium. Added cations and anions catalysed and inhibited the reaction rate respectively. Based on spectroscopic investigation and kinetic pieces of evidence from the Michaelis–Menten plot and effect of added ions, an outer sphere mechanism has been rationalised for the reaction. Keywords Electron transfer · Iodide ion · Kinetics · Mechanism · Tris(1,10-phenanthroline)cobalt(III) complex
1 Introduction Electron Transfer reactions just as the name implies involves the transfer of electron(s) from one specie (reductant) to another (oxidant). The comprehension of this concept is very vital to chemists in the context of energy transduction, corrosion processes, and metallurgy among others [1, 2]. Electron transfer reactions of transition metal complexes are usually accompanied by a change in the oxidation state of the metal atom and the overall charge on the complex ion. Electron transfer reactions are also important in many biochemical and biological processes including enzymatic reactions, collagen synthesis, steroid metabolism, the immune response, drug activation, neurotransmitter metabolism, nitrogen fixation, respiration and photosynthesis [3]. The study of the rate at which reactions including electron transfer reaction occur is very important and cannot * D. E. Arthur [email protected] 1
Department of Chemistry, Baze University, Abuja, Nigeria
Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria
2
be over-emphasised and that is the basis of kinetic studies. Kinetic studies also deal with the factors that influences the rate of reaction such as temperature, concentration, pressure, effect of catalyst etc.[4]. The knowledge of the variation and effect of these factors on reaction rate can aid proper interpretation of stepwise elementary steps a reaction undertakes which constitute its mechanism [5]. Based on these, the Nobel Prize winner in Chemistry of 1983, Henry Taube on his experimental facts has successfully classified these reaction mechanisms into two broad mechanistic pathways: Inner-sphere and outer-sphere mechanism of electron transfer [6]. He assigned oxidation–reduction reac
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