Solvation in ionic liquids: an EPR study

Noel, M.; Allendoerfer, Robert D.; Osteryoung, R. A.

doi:10.1021/j100184a070

Cited by 61 publications

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“…Cautionary remarks regarding over-interpretation of these absolute t R values not withstanding, it is nevertheless useful to compare the numbers reported here with those obtained in other ionic liquids using the same approach. Noel et al measured t R = 0.08 ns for TEMPO in the binary ionic liquid [C 2 mim][Cl]/AlCl 3 (303 K), [5] and coefficients of 0.46-1.70 ns in a range of imidazolium and tetraalkylammonium RTILs have been reported for the related compound 4-amino-2,2,6,6-tetramethylpiperidine-N-oxyl (293 K), [4] thus the present findings are consistent with the literature. Turning to the activation energies, the situation is not as straightforward as in the case of translational diffusion.…”

Section: à11mentioning

confidence: 99%

“…While ESR has seldom been employed to study ionic liquids, the reports that have appeared describe the successful application of this methodology for accessing rotational solvent-solute parameters. [4,5] The stable free radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) was selected as the diffusional probe for this study. In addition to possessing a simple and well-characterised ESR spectrum, [6] it is also capable of being oxidised electrochemically and reversibly through the loss of one electron to yield the corresponding oxammonium cation (Scheme 1).…”

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An Electrochemical and ESR Spectroscopic Study on the Molecular Dynamics of TEMPO in Room Temperature Ionic Liquid Solvents

et al. 2005

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The field of room temperature ionic liquid (RTIL) research is currently very active, with the potential of fashioning "greener" alternatives to traditional molecular solvents driving intensive studies into their applications across many chemical disciplines, which include the synthetic and electrochemical industries. [1,2] Characterisation of the transport properties and solvating ability of this new class of reaction media will presumably form an important part in realising this endeavour to its full potential, although to date, reports on more fundamental investigations of this nature have been less common. To aid in this effort, we recently explored the temperature dependence of the translational diffusion of probe molecules N,N,N',N'-tetramethyl-para-phenylenediamine, its radical cation and dication in several RTIL solvents, by means of a chronoamperometric technique. [3] Amongst these species, the variation in translational diffusion coefficient, D T , with temperature in each ionic liquid was found to obey an Arrhenius relation of general form [Eq. (1)]:where E a represents the activation energy associated with the temperature-dependent process, f 0 is a constant of proportionality and, in the current context, f = 1/D T . Furthermore, the diffusional activation energies calculated by plotting ln f versus 1/T and measuring the slope were, for a given RTIL, largely independent of solute charge or size. Subjecting the measured viscosity, h, of the ionic liquids at each temperature to the same Arrhenius-type analysis [with f = h in Equation (1)] systematically yielded an activation energy of viscous flow that also closely resembled this diffusional activation energy. This implies an inverse linear relationship between translational diffusion coefficient and solvent viscosity, akin to that commonly observed in conventional molecular solvents and generally formulated in terms of the Stokes-Einstein equation [Eq. (2)]:where a is the hydrodynamic radius of the (spherical) diffusing molecule. The current report aims to build on this work by now expanding the investigation to include rotational diffusion. The equivalent hydrodynamic description of molecular rotation in a liquid is given by the Debye-Stokes-Einstein equation [Eq. (3)]:where D R and t R are termed the rotational diffusion coefficient and rotational correlation coefficient, respectively. Note that an inverse linear relationship between rotational diffusion coefficient and solvent viscosity is again predicted. For sufficiently viscous solvents, electron spin resonance (ESR) can be utilised to measure the rotational correlation coefficient of paramagnetic species via analysis of the spectral line-shapes, a technique which exploits the fact that restricted molecular tumbling of the rotational probe leads to an incomplete averaging of the ESR signal on the experimental timescale, ultimately manifesting as asymmetry in the resulting spectrum. While ESR has seldom been employed to study ionic liquids, the reports that have appeared describe the successful app...

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Section: à11mentioning

confidence: 99%

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An Electrochemical and ESR Spectroscopic Study on the Molecular Dynamics of TEMPO in Room Temperature Ionic Liquid Solvents

et al. 2005

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“…Surprisingly, little work on electrochemical EPR has been undertaken in these media. Allendoerfer and Osteryoung have pioneered this area [132], primarily focusing upon measurements on polymers (such as polypyrrole [133] and polyaniline [134]) in 1-methyl-3-ethylimidazolium chloride and aluminum chloride.…”

Section: Electrochemical Epr In Ionic Liquidsmentioning

confidence: 99%

EPR Spectroscopy in Electrochemistry

Wadhawan

Compton

2003

Encyclopedia of Electrochemistry

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The sections in this article are Introduction Principles of EPR Spectroscopy EPR Theory The g ‐value Linewidths Spin‐lattice Relaxation Spin–spin Relaxation Hyperfine Structure EPR Instrumentation In Situ Electrochemical EPR : Cell Design The Bard–Goldberg Cell Cell Design Typical Applications The Allendoerfer Cells Cell Design The Coaxial Cell Application The Loop‐gap Resonator Cell Application The Channel Electrode Cell Cell Design Application The Albery In Situ Tube Electrode Cell Cell Design Application The In Situ Coaxial Flow Cell Cell Design Application The Bond In Situ Microelectrode Cell Cell Design Application The In Situ Wall‐jet Electrode Cell Cell Design Application The Dunsch–Petr–Neudeck Cell for In Situ UV ‐ VIS EPR Spectroelectro‐ chemistry Cell Design Application The Dryfe–Webster Cell for Charge Transfer Across a Liquid|Liquid Phase Boundary Cell Design Typical Applications Illustrative Examples of EPR in Electrochemistry Radical and Radical Ion Identification The Anodic Oxidation of para ‐Aminodiphenylamine ( PAD ) The Reduction of Dicyanobenzene The Reduction of C 60 Spin Trapping Electrode Reaction Kinetics and Mechanism EC Versus ECE ECE Versus DISP 1 EC ′ Comproportionation Reactions Photoelectrochemical EPR Modified Electrodes Electrochemical EPR in Ionic Liquids Conclusion Acknowledgments

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“…Stable radicals, so called spin probes, have been successfully used as model compounds to describe the mobility of reactive species in the ionic liquids. [8][9][10][11][12][13][14][15][16][17][18][19][20] Furthermore, the isotropic hyperfine coupling constants of the stable radicals give information about micropolarity of the surrounding matrix. 13,16,20-22 2,2,6,6-Tetramethylpiperidine-1-yloxyl derivatives are examples for spin probes, which have been successfully applied for the investigation of ionic liquids.…”

Section: Introductionmentioning

confidence: 99%