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Title: Electron transfer reactivity of the aqueous iron(IV)–oxo complex. Outer-sphere vs proton-coupled electron transfer

Here, the kinetics of oxidation of organic and inorganic reductants by aqueous iron(IV) ions, Fe IV(H 2O) 5O 2+ (hereafter Fe IV aqO 2+), are reported. The substrates examined include several water-soluble ferrocenes, hexachloroiridate(III), polypyridyl complexes M(NN) 3 2+ (M = Os, Fe and Ru; NN = phenanthroline, bipyridine and derivatives), HABTS–/ABTS 2–, phenothiazines, Co II(dmgBF 2) 2, macrocyclic nickel(II) complexes, and aqueous cerium(III). Most of the reductants were oxidized cleanly to the corresponding one-electron oxidation products, with the exception of phenothiazines which produced the corresponding oxides in a single-step reaction, and polypyridyl complexes of Fe(II) and Ru(II) that generated ligand-modified products. Fe IV aqO 2+ oxidizes even Ce(III) (E 0 in 1 M HClO 4 = 1.7 V) with a rate constant greater than 10 4 M –1 s –1. In 0.10 M aqueous HClO 4 at 25 °C, the reactions of Os(phen) 3 2+ (k = 2.5 × 10 5 M –1 s –1), IrCl 6 3– (1.6 × 10 6), ABTS 2– (4.7 × 10 7), and Fe(cp)(C 5H 4CH 2OH) (6.4 × 10 7) appear to take place by outer sphere electron transfer (OSET). The rate constants for the oxidation of Os(phen) 3 2+ and ofmore » ferrocenes remained unchanged in the acidity range 0.05 < [H+] < 0.10 M, ruling out prior protonation of Fe IV aqO 2+ and further supporting the OSET assignment. A fit to Marcus cross-relation yielded a composite parameter (log k 22 + E 0 Fe/0.059) = 17.2 ± 0.8, where k 22 and E 0 Fe are the self-exchange rate constant and reduction potential, respectively, for the Fe IV aqO 2+/Fe III aqO + couple. Comparison with literature work suggests k 22 < 10 –5 M –1 s –1 and thus E 0(Fe IV aqO 2+/Fe III aqO +) > 1.3 V. For proton-coupled electron transfer, the reduction potential is estimated at E 0 (Fe IV aqO 2+, H +/Fe III aqOH 2+) ≥ 1.95 V.« less
Authors:
 [1] ;  [1] ;  [1]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
Publication Date:
Report Number(s):
IS-J-8983
Journal ID: ISSN 0020-1669
Grant/Contract Number:
AC02-07CH11358
Type:
Accepted Manuscript
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Name: Inorganic Chemistry; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1259478

Bataineh, Hajem, Pestovsky, Oleg, and Bakac, Andreja. Electron transfer reactivity of the aqueous iron(IV)–oxo complex. Outer-sphere vs proton-coupled electron transfer. United States: N. p., Web. doi:10.1021/acs.inorgchem.6b00966.
Bataineh, Hajem, Pestovsky, Oleg, & Bakac, Andreja. Electron transfer reactivity of the aqueous iron(IV)–oxo complex. Outer-sphere vs proton-coupled electron transfer. United States. doi:10.1021/acs.inorgchem.6b00966.
Bataineh, Hajem, Pestovsky, Oleg, and Bakac, Andreja. 2016. "Electron transfer reactivity of the aqueous iron(IV)–oxo complex. Outer-sphere vs proton-coupled electron transfer". United States. doi:10.1021/acs.inorgchem.6b00966. https://www.osti.gov/servlets/purl/1259478.
@article{osti_1259478,
title = {Electron transfer reactivity of the aqueous iron(IV)–oxo complex. Outer-sphere vs proton-coupled electron transfer},
author = {Bataineh, Hajem and Pestovsky, Oleg and Bakac, Andreja},
abstractNote = {Here, the kinetics of oxidation of organic and inorganic reductants by aqueous iron(IV) ions, FeIV(H2O)5O2+ (hereafter FeIVaqO2+), are reported. The substrates examined include several water-soluble ferrocenes, hexachloroiridate(III), polypyridyl complexes M(NN)32+ (M = Os, Fe and Ru; NN = phenanthroline, bipyridine and derivatives), HABTS–/ABTS2–, phenothiazines, CoII(dmgBF2)2, macrocyclic nickel(II) complexes, and aqueous cerium(III). Most of the reductants were oxidized cleanly to the corresponding one-electron oxidation products, with the exception of phenothiazines which produced the corresponding oxides in a single-step reaction, and polypyridyl complexes of Fe(II) and Ru(II) that generated ligand-modified products. FeIVaqO2+ oxidizes even Ce(III) (E0 in 1 M HClO4 = 1.7 V) with a rate constant greater than 104 M–1 s–1. In 0.10 M aqueous HClO4 at 25 °C, the reactions of Os(phen)32+ (k = 2.5 × 105 M–1 s–1), IrCl63– (1.6 × 106), ABTS2– (4.7 × 107), and Fe(cp)(C5H4CH2OH) (6.4 × 107) appear to take place by outer sphere electron transfer (OSET). The rate constants for the oxidation of Os(phen)32+ and of ferrocenes remained unchanged in the acidity range 0.05 < [H+] < 0.10 M, ruling out prior protonation of FeIVaqO2+ and further supporting the OSET assignment. A fit to Marcus cross-relation yielded a composite parameter (log k22 + E0Fe/0.059) = 17.2 ± 0.8, where k22 and E0Fe are the self-exchange rate constant and reduction potential, respectively, for the FeIVaqO2+/FeIIIaqO+ couple. Comparison with literature work suggests k22 < 10–5 M–1 s–1 and thus E0(FeIVaqO2+/FeIIIaqO+) > 1.3 V. For proton-coupled electron transfer, the reduction potential is estimated at E0 (FeIVaqO2+, H+/FeIIIaqOH2+) ≥ 1.95 V.},
doi = {10.1021/acs.inorgchem.6b00966},
journal = {Inorganic Chemistry},
number = ,
volume = ,
place = {United States},
year = {2016},
month = {6}
}