Observation and Simulation of the Transient Anion Oligomers (LiClO4)n (n = 1-4) in Diethyl Carbonate LiClO4 Solutions

Furong Wang 1 Pascal Pernot 1 Pierre Archirel 1 Daniel Ortiz 2 Sophie Le Caër 2 Mehran Mostafavi 1, *
* Auteur correspondant
2 LIONS - Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : NMR measurements show that diethyl carbonate (DEC, a solvent with a low dielectric constant) solutions of LiClO4 contain (LiClO4)n oligomers. The reduction of these species by solvated electrons and pre-solvated electrons is followed by picosecond pulse radiolysis measurements. The data analysis shows that several anions absorbing in the NIR and visible range are formed after the 7 ps electron pulse. In contrast with THF solutions of LiClO4, the anionic monomer (LiClO4)- is not observed in DEC solutions. This is due to the fact that DEC is a non-polar solvent favoring the clustering of the monomers in the non-irradiated solution as shown by NMR results, and also due to the instability of the anionic monomer. The absorption spectra of the anionic dimer (LiClO4)2-, trimer (LiClO4)3- and tetramer (LiClO4)4- are clearly observed in NIR and in visible ranges. Compared to the results obtained for the same system in THF, and in agreement with simulated absorption spectra, the experimental results show that the absorption bands are shifted to the blue when n increases. The kinetics recorded for the molar LiClO4 solution indicate that the solute is only under the form of oligomers (LiClO4)n with a large n value and that the reduced species absorb weakly in the visible. Lastly, and contrarily to what is known for well separated ions in polar solvents, it is shown that the (LiClO4)n- anions are not stable with respect to self-reduction, leading to the decomposition of perchlorate anions. In this reaction the perchlorate anion ClO4- is reduced by the Li atom into a chlorate anion ClO3-. This is proved by the presence of ClO3- and of chlorinated species detected by mass spectrometry measurements in irradiated DEC solutions containing LiClO4.
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The Journal of physical chemistry, American Chemical Society (ACS), 2017, 121, pp.7464-7472. 〈http://dx.doi.org/10.1021/acs.jpcb.7b04982〉. 〈10.1021/acs.jpcb.7b04982〉
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Furong Wang, Pascal Pernot, Pierre Archirel, Daniel Ortiz, Sophie Le Caër, et al.. Observation and Simulation of the Transient Anion Oligomers (LiClO4)n (n = 1-4) in Diethyl Carbonate LiClO4 Solutions. The Journal of physical chemistry, American Chemical Society (ACS), 2017, 121, pp.7464-7472. 〈http://dx.doi.org/10.1021/acs.jpcb.7b04982〉. 〈10.1021/acs.jpcb.7b04982〉. 〈cea-01566287〉

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