15276-15-0Relevant academic research and scientific papers
Reduction of hexaammineruthenium(III) ions by a series of tris(polypyridyl)chromium(II) ions - Revisiting the Cr(NN)33+/2+ self-exchange rate
Zahir
, p. 1124 - 1127 (2007/10/03)
The kinetics of the outer-sphere oxidation of Cr(NN)32+ ions (NN = 2,2′-bipyridine, 1,10-phenanthroline, and their substituted analogs) by hexaammineruthenium(III) was studied using laser flash photolysis. The Cr(NN)32+ ions were generated via the reductive quenching of the *Cr(NN)33+ excited states by oxalate ions or by H2edta2-. The second-order rate constants were found to vary with the driving force of the reaction. The rate constants increase from (7.1 ± 0.5) × 106 M-1 s-1 for Cr(5-Clphen)32+ to (2.6 ± 0.2) × 108 M-1 s-1 for Cr(4,7-Me2phen)32+. The self-exchange rate constant for the couple (Cr(NN)33+/2+) was calculated by applying Marcus cross relation to present and other known reactions of Cr(NN)3n+ ions, where n = 3 or 2 with various reactants and is estimated to be (6 ± 4) × 107 M-1 s-1.
Oxidation of a series of tris(polypyridyl)chromium(II) ions by several cobalt(III) complexes
Zahir, Khurram,Espenson, James H.,Bakac
, p. 3144 - 3146 (2008/10/08)
The kinetics of the outer-sphere oxidation of Cr(NN)32+ ions (NN = 2,2′-bipyridine, 1,10-phenanthroline, and their substituted derivatives) by tris(chelating ligand) complexes of Co(III) were studied. The second-order rate constants increase with the driving force of the reaction. The rate constants for Co(en)33+ at 23 ± 2°C increase from 2.2 (±0.3) × 103 M-1 s-1 for Cr(bpy)32+ to 1.1 (±0.2) × 105 M-1 s-1 for Cr(4,7-Me2-phen)32+ and agree very well with the values calculated by the Marcus cross relation. For Co(bpy)33+ and Co(phen)33+, on the other hand, the experimental rate constants are lower than the calculated values. It is suggested that the reactions of these two species are mildly nonadiabatic, the extent of nonadiabaticity increasing with an increase in the standard free energy of the reaction.
Charge-Transfer Perturbations of the Electronic Contributions to Electron-Transfer Reactions. Enhanced Donor-Acceptor Couplings Mediated by Coordinated Ligands
Endicott, John F.,Ramasami, T.
, p. 3740 - 3747 (2007/10/02)
The factors contributing to variations in the adiabaticity of a series of Co(III)-Co(sep)(2+) (sep= (S)-1,3,6,8,10,13,16,19-octaazabicycloeicosane) cross-reactions have been investigated.Coordinated ligands can be effective in making the electron-transfer rates more adiabatic by altering the electronic structure of the complex and/or by contributing to intermolecular charge-transfer interactions.Alterations of the coordinated ligands change both the ligand field and the charge-transfer excited states of the Co(III) acceptor, and the contributions of each kind of excited state perturbation must be considered in evaluating rate patterns.For Co(NH3)5X(2+) oxidants, the inferred values of the electronic transmission coefficient, κel, increase systematically through the series X=CN, Cl, Br, N3, and I with the smallest value of κel being ca. 10-3 and the largest approaching unity.Simple models are proposed which account for the variations in κel based on the perturbational effects of ligand to metal charge transfer and triplet ligand field excited states on the electron exchange integral coupling reactants and products.
