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  • Chem Sci Trans., 2013, 2(S1),  pp S65-S70  

    DOI:10.7598/cst2013.13

    Research Article

    Modeling Analysis of the Photoreduction of Cobalt(III) Speciation via (CoIII-I-) Ion Pair Formation in Water-1,4-Dioxane Mixtures with XRPD and Voltammetric Studies

  • L. DEVARAJ STEPHEN and K. ANBALAGAN
  • Department of Chemistry, SRM Valliammai Engineering College, Chennai-603203, India
    Department of Chemistry, Pondicherry University, Puducherry- 605 014, India
  • Abstract

    Ion pair charge transfer (IPCT) reaction has been studied on the reduction of CoIII centre in coordination compounds with reference to solvent medium and structure of the complex. A series of CoIII(L)33+
    (L = (NH3)2, en, pn, tn and bn) were prepared, characterized and the structures of the complexes were refined using powder XRD data. CoIII(L) 33+ crystallizes in distorted monoclinic system with = 92.93 (1) to 113.00 (2)Ο. A combination of powder XRD and cyclic voltammetric technique is shown to be methodologically important and complementary for the understanding of reduction property of CoIII centre. The voltammetric measurements of CoIII(L)33+ have shown one irreversible Co(III) → Co(II) reduction of metal centre and the peak positions of the complexes are localized due to strained ligand. Quantum yield for 254 nm excitation of CoIII(L) 33+ (L = (NH3)2, en, pn, tn and bn) in water-1,4-dioxane mixtures (Diox = 0, 5, 10, 15, 20, 25 and 30% (v/v)) were also derived for all the complexes in presence of added iodide ion, in which CoIII is reduced via {CoIIIL33+, I-} ion-pair formation. The photoactive state is ion-pair charge transfer transition state and the quantum efficiency is solvent dependent. That is, ΦCo(II) in water Diox (100:0 (v/v)) is less than that in water Diox (70:30 (v/v)). That is, change in ΦCo(II) is consistent with observed increase in xDiox of the medium. An elaboration on binary solvent modified ΦCo(II) in terms of correlation relationships using solvent empirical parameters εr, Y, ETN, DNN, α, and π* provides a model to understand solvent medium participation. Application of this method involving model equation of the form YS = Y0 + Σni=1aiΧi helps the binary solvent effect on {CoIII(L)33+, I-} ion pair into CoII product formation efficiency. The photoreduction proceeds through long-range and short range solvation mechanisms. Regression methods were attempted to quantify the solvation effect.

    Keywords

    Modeling Analysis, Ion pair charge transfer, Photoreduction, Water-1,4-dioxane mixtures

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