I= KINETIC STUDY OF ELECTRON TRANSFER REACTIONS BETWEEN SOME TRANSITION METAL COMPLEXES AND INVESTIGATION OF FACTORS INFLUENCING THE ELECTRON TRANSFER PROCESSES
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Title of Thesis
KINETIC STUDY OF ELECTRON TRANSFER REACTIONS BETWEEN SOME TRANSITION METAL COMPLEXES AND INVESTIGATION OF FACTORS INFLUENCING THE ELECTRON TRANSFER PROCESSES

Author(s)
Muhammad Akhyar Farrukh
Institute/University/Department Details
University of Karachi/ Department of Chemistry
Session
2003
Subject
Number of Pages
211
Keywords (Extracted from title, table of contents and abstract of thesis)
electron transfer reactions, transition metal, electron transfer, bis(asetylacetonato) diaquo manganese(iii), sodium thiosulfate, tris(1,10-orthophenanthroline)iron(iii), potassium hexacyanoferrate(ii), bis(π-cyclopentadienyl)iron(ii), iron, dielectric constant, ionic strength

Abstract
Kinetic study of the reduction of bis(asetylacetonato) diaquo manganese(III) complex by sodium thiosulfate and tris(1,10-orthophenanthroline)iron(III) complex with potassium hexacyanoferrate(II) and bis(π-cyclopentadienyl)iron(II) complexes has been investigated. The rates of reduction have been explained in terms of free energy changes of the reactions and entropy of activation in connection with different theories of electron transfer processes. The findings of the study strongly support the provisions of Frank-Condon principle, Marcus and electron tunneling theories for outer sphere electron transfer mechanism

Bis(acetylacetonato) diaquomanganese(III) complex (E = 0.40V) was prepared in perchloric acid medium. Kinetic order of the reduction of this complex with thiosulfate (E = 0.08V) was established. It was found that the reaction follows first order kinetics in complex, fractional order in thiosulfate and [H+]. The redox mechanism has been explained hrough the formation of an intermediate ion pair resulting from the direct interaction of oxidizing and reducing species, which gets dissociated into products. At pH 3.0 and 30+0.50ºC the rate law is suggested to be

However at pH values above 5, kobs was found to alter. The new value of kobs was found to be Activation parameters have also been computed and were found to be Ea =15.36 kJ mol-1, ∆Gº=-30.88 kJ mol-1, ∆H# =12.69 kJmol-1 ∆S#=-179JK-1 mol-1 and ∆G#=66.03kJ mol-1.

The kinetics of reduction of tris(1,10-orthophenanthroline)iron(III) ion by hexacyanoferrate (II) ion has been spectrophotometrically investigated in aqueous medium, at 30±0.5ºC and correlated with the redox potential values. Whose standard cell potential values are 1.147V and 0.358V respectively. Measurements were recorded under pseudo-first order conditions. The rate of electron transfer between potassium hexacyanoferrate(II) and tris(1,10-orthophenanthroline)iron(III) was measured at different pH values viz 3.6, 3.8, 4.0 and 4.2. It was found that the rate of reaction increased with the increase of pH and inverse fractional order was found in [H+]. The rate law is suggested to be, where K1 is the specific rate constant for the reaction [Fe(CN)6]4-+[Fe(0-phen)3]3+→[Fe(CN)6]3-+[Fe(0-phen)3]2+ having the value of 8.33 X107 dm3 mol-1 s-1 and K is the equilibrium constant of protonated and deprotonated forms of hexacyanoferrate(II) complex having the value of 2.1X104 M-1. Formal potential values of hexacyanoferrate(III) / hexacyanoferrate(II) system were also determined in varying concentrations of acida like HCIO4, HCI, HNO3, H2SO4. The formal potential values were recorded and found to be higher than the corresponding standard redox potential value potentials and demonstrates that oxidation potential of potassium hexacyanoferrate(II) decreases with decrease in pH. Different thermodynamics functions for the reaction were Ea =9.85 kJ mol-1, ∆Gº=-76.14 kJ mol-1, ∆H# =7.69 kJmol-1 ∆S#=-189JK-1 mol-1 and ∆G#=65.01kJ mol-1.

Kinetic study of the redox reaction between tris(a,10-orthophenanthroline)iron(III) ion and bis(π-cyclopentadienyl)iron(II), whose standard cell potential values are 1.147V and 0.40V respectively, was studied at pH 3.6 and 30±0.5ºC. the reaction was found to be first order with respect to each reactant having the value of second order rate constant of 5X106 dir3 mol-1 s-1. Thrmodynamic functions were Ea =6.78 kJ mol-1, ∆Gº=-72.08 kJ mol-1, ∆H# =4.32 kJmol-1 ∆S#=-208JK-1 mol-1 and ∆G#=66.45kJ mol-1.

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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents 0
151.01 KB
2 1 Electron Transfer Reactions 1
415.88 KB
  1.1 Mechanisms Of Electron Transfer Reactions 5
  1.2 Influencing Electron Transfer Reactions Through Change In Acidity Of The Medium 42
  1.3 Suitable Reductants 45
  1.4 Manganese 47
  1.5 Iron 48
3 2 Experimental 51
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  2.1 Reduction Of [ Mn ( acac )2(H2O)2]+with[S2O32-] 51
  2.2 Reduction Of [Fe(0-phen)3]3+with[Fe(CN)6]4- and [Fe(C5H5)2] 59
4 3 Results And Discussion 34
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  3.1 Reaction Between [ Mn ( acac )2(H2O)2]+and[S2O32-] 51
  3.2 Reduction Of [Fe(0-phen)3]3+with[Fe(CN)6]4- and [Fe(C5H5)2] 59
5 4 Conclusions 179
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  4.1 Dielectric Constant 179
  4.2 Ionic Strength 180
  4.3 Libby’s Theoretical Discussion 182
  4.4 Entropy Of Activation 182
  4.5 Marcus Theory 186
  4.6 Electron Tunneling Theory 187
  4.7 Molecular Orbital Theory 189
6 5 References 195
123.23 KB