Reversible dimerization of anion radicals: Studies of two cyanopyridines

Macı́as-Ruvalcaba, Norma A.; Evans, Dennis H.

doi:10.1016/j.jelechem.2010.07.019

Cited by 14 publications

(19 citation statements)

References 30 publications

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“…We assume that upon the cathodic reduction the initially generated radical anions from the 1 h –6 h and 1 f –6 f samples rapidly dimerize to the corresponding EPR-silent stable σ-dimer dianions (Scheme ). Similar indications have already been reported in the literature by other systems. ,,,, …”

Section: Resultssupporting

confidence: 91%

“…Similar indications have already been reported in the literature by other systems. 21,24,26,33,34 More information was obtained from in situ EPR/UV−vis electrochemistry of 1f quinolone in 0.2 M TBAPF 6 /DMSO solution (scan rate 4 mV s −1 ) performed in four consecutive voltammetric cycles (Figures 4 and 5 and Figure 4S in the Supporting Information). Results from the first cycle are presented in Figure 4a Figure 4b), the band at 450 nm decreases, and two new bands at 335 and 380 nm are evident.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Stable Radical Trianions from Reversibly Formed Sigma-Dimers of Selenadiazoloquinolones Studied by In Situ EPR/UV–vis Spectroelectrochemistry and Quantum Chemical Calculations

et al. 2012

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The redox behavior of the series of 7-substituted 6-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-h]quinolines and 8-substituted 9-oxo-6,9-dihydro[1,2,5]selenadiazolo[3,4-f]quinolines with R(7), R(8) = H, COOC(2)H(5), COOCH(3), COOH, COCH(3), and CN has been studied by in situ EPR and EPR/UV-vis spectroelectrochemistry in dimethylsulfoxide. All selenadiazoloquinolones undergo a one-electron reduction process to form the corresponding radical anions. Their stability strongly depends on substitution at the nitrogen atom of the 4-pyridone ring. The primary generated radical anions from N-ethyl-substituted quinolones are stable, whereas for the quinolones with imino hydrogen, the initial radical anions rapidly dimerize to produce unusually stable sigma-dimer (σ-dimer) dianions. These are reversibly oxidized to the initial compounds at potentials considerably less negative than the original reduction process in the back voltammetric scan. The dimer dianion can be further reduced to the stable paramagnetic dimer radical trianion in the region of the second reversible reduction step. The proposed complex reaction mechanism was confirmed by in situ EPR/UV-vis cyclovoltammetric experiments. The site of the dimerization in the σ-dimer and the mapping of the unpaired spin density both for radical anions and σ-dimer radical trianions with unusual unpaired spin distribution have been assigned by means of density functional theory calculations.

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Section: Resultssupporting

confidence: 91%

Section: ■ Results and Discussionmentioning

confidence: 99%

Stable Radical Trianions from Reversibly Formed Sigma-Dimers of Selenadiazoloquinolones Studied by In Situ EPR/UV–vis Spectroelectrochemistry and Quantum Chemical Calculations

et al. 2012

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“…It should be noted that this study by no means rules out the possibility of dimerization occurring with some quinone radicals. Indeed, both π and σ dimerization of the radical ions of quinones , and related species , is well-documented. Instead, we are simply pointing out that dimerization does not explain all the irregularities observed with quinone voltammetry and that reaction with surface groups on GC electrodes is another cause of irregular behavior that should be considered.…”

Section: Discussionmentioning

confidence: 99%

The Effect of Glassy Carbon Surface Oxides in Non-Aqueous Voltammetry: The Case of Quinones in Acetonitrile

et al. 2014

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Glassy carbon (GC) electrodes are well-known to contain oxygenated functional groups such as phenols, carbonyls, and carboxylic acids on their surface. The effects of these groups on voltammetry in aqueous solution are well-studied, but there has been little discussion of their possible effects in nonaqueous solution. In this study, we show that the acidic functional groups, particularly phenols, are likely causes of anomalous features often seen in the voltammetry of quinones in nonaqueous solution. These features, a too small second cyclic voltammetric wave and extra current between the two waves that sometimes appears to be a small, broad third voltammetric wave, have previously been attributed to different types of dimerization. In this work, concentration-dependent voltammetry in acetonitrile rules out dimerization with a series of alkyl-benzoquinones because the anomalous features get larger as the concentration decreases. At low concentrations, solution bimolecular reactions will be relatively less important than reactions with surface groups. Addition of substoichiometric amounts of naphthol at higher quinone concentrations produces almost identical behavior as seen at low quinone concentrations with no added naphthol. This implicates hydrogen bonding and proton transfer from the surface phenolic groups as the cause of the anomalous features in quinone voltammetry at GC electrodes. This conclusion is supported by the perturbation of surface oxide coverage on GC electrodes through different electrode pretreatments.

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“…51, 53, 56–58 Most reported radical‐radical coupling reactions are fully irreversible but the reversibility of σ‐dimerization processes has also been postulated for various radicals59–68 including pyridinyl derivatives 53. 61, 69–74 The proposed dimeric structures produced from 6 2 . through coupling between the 2–4′, 2–2′, or 4–4′ positions of both pyridinyl radicals are depicted in Scheme ( 7 , 8 , and 9 ).…”

Section: Resultsmentioning

confidence: 99%

Chemically and Electrochemically Triggered Assembly of Viologen Radicals: Towards Multiaddressable Molecular Switches

Kahlfuss

Métay

Duclos

et al. 2014

Chemistry A European J

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We have established that bipyridinium radicals can be reversibly π-dimerized under the combined effects of chemical (proton transfer) and electrochemical (electron transfer) stimuli. Our investigations also led to the discovery that a bis-pyridinyl appended calixarene intermediate is involved in a fully reversible redox-triggered σ-dimerization process. The structure of the most stable intramolecular σ-dimer was provided by computational chemistry and its complete conversion into a noncovalent π-dimer could be triggered chemically by addition of protons, leading to the formation of protonated cation radicals. Theoretical data collected with the N-methylated and N-protonated π-dimers also support the existence of multivariant orientations in π-bonded dimers of viologen cation-radicals.

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Reversible dimerization of anion radicals: Studies of two cyanopyridines

Cited by 14 publications

References 30 publications

Stable Radical Trianions from Reversibly Formed Sigma-Dimers of Selenadiazoloquinolones Studied by In Situ EPR/UV–vis Spectroelectrochemistry and Quantum Chemical Calculations

Stable Radical Trianions from Reversibly Formed Sigma-Dimers of Selenadiazoloquinolones Studied by In Situ EPR/UV–vis Spectroelectrochemistry and Quantum Chemical Calculations

The Effect of Glassy Carbon Surface Oxides in Non-Aqueous Voltammetry: The Case of Quinones in Acetonitrile

Chemically and Electrochemically Triggered Assembly of Viologen Radicals: Towards Multiaddressable Molecular Switches

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