Mechanistic studies of the selective reduction of ruthenium(III) containing trinuclear oxo complexes by l-ascorbic acid in aqueous solution
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The reduction of the Ru(III) oxo-centred trinuclear acetate cations, [Ru3(μ3-O)(μ2-CH3CO2)6(H2O)3]+ and [Ru2Cr(μ3-O)(μ2-CH3CO2)6(H2O)3]+, by the biological reductant l-ascorbic acid was studied spectrophotometrically under pseudo first-order conditions over the ranges 3.05 ≤ pH ≤ 4.83 (acetate buffer), 15 °C ≤ θ ≤ 30 °C and at I = 0.5 mol dm−3 (NaClO4). The first electron transfer in the redox process resulted in mixed-valence species [Ru2M(μ3-O)(μ2-CH3CO2)6(H2O)3]0, where M = Ru or Cr, followed by the slow consecutive reduction of other Ru(III) ions. The kinetics of the formation of the mixed-valence species was studied in detail, and a mechanism in support of these data is proposed. The intricate mechanistic details of the subsequent reactions are unclear as the spectral characteristics of the species involved could not be resolved from those of the first intermediate. The final products, however, were found to be Ru(II) (and Cr(III) for the mixed-metal species) in acetate buffer. The electron-transfer mechanism has been proposed to be inner-sphere, as deduced from Marcus cross-relationship. In an aqueous acetate buffer at I = 1.0 mol dm−3 (NaClO4), the cyclic voltammograms of the complexes were found to be quasi-reversible and pH dependent and have values of 0.18 and 0.19 V (relative to SHE) at pH = 3.41 for the [Ru3(μ3-O)(μ2-CH3CO2)6(H2O)3]+ and [Ru2Cr(μ3-O)(μ2-CH3CO2)6(H2O)3]+ cations, respectively.
KeywordsRuthenium Complex Cation Observe Rate Constant 8453A Diode Array Spectrophotometer Predict Rate Constant
The authors would like to thank Professor Willem H. Mulder and Ms Kerry-Ann Green for their valuable comments to this work, and The University of the West Indies (Mona) Board of Graduate Studies and Research, for funding.
- 25.Lawrence MAW, Maragh PT, Dasgupta TP (2012) Inorg Chim Acta 388:88–97Google Scholar
- 28.Dawson RMC, Elliott DC, Elliott WH, Jones KM (eds) (1969) Data for biochemical research, 2nd edn. Oxford University Press, OxfordGoogle Scholar
- 31.Burgess J (2005) Ions in Solution Basic: Principles of Chemical Interaction, 2nd edn. Horwood Publishing, ChichesterGoogle Scholar
- 34.Cotton FA, Wilkinson G, Murillo CA, Bochmann M (1999) Advanced inorganic chemistry, 6th edn. Wiley, NYGoogle Scholar
- 46.Zoski CG (2007) Handbook of electrochemistry. Elsevier, New YorkGoogle Scholar