Observation and Simulation of Transient Anion Oligomers (LiClO₄)_n^– (n = 1–4) in Diethyl Carbonate LiClO₄ Solutions

Abstract

NMR measurements show that diethyl carbonate (DEC, a solvent with a low dielectric constant) solutions of LiClO contain (LiClO) oligomers. The reduction of these species by solvated and presolvated electrons is followed by picosecond pulse radiolysis measurements. The data analysis shows that several anions absorbing in the near-infrared (NIR) and visible range are formed after the 7 ps electron pulse. In contrast with tetrahydrofuran (THF) solutions of LiClO, the anionic monomer (LiClO) is not observed in DEC solutions. This is due to the fact that DEC is a nonpolar solvent favoring the clustering of monomers in the nonirradiated solution, as shown by NMR results, and also due to the instability of the anionic monomer. The absorption spectra of the anionic dimer (LiClO), trimer (LiClO), and tetramer (LiClO) are clearly observed in NIR and 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 end of the spectrum when n increases. The kinetics recorded for the molar LiClO solution indicates that the solute is only in the form of oligomers (LiClO) with a large n value and that the reduced species absorb weakly in the visible region. Lastly, and contrary to what is known for well-separated ions in polar solvents, it is shown that the (LiClO) anions are not stable with respect to self-reduction, leading to the decomposition of perchlorate anions. In this reaction, the perchlorate anion ClO is reduced by the Li atom into a chlorate anion ClO. This is proved by the presence of ClO and chlorinated species detected by mass spectrometry measurements in irradiated DEC solutions containing LiClO.

Picosecond Pulse Radiolysis Study on the Radiation-Induced Reactions in Neat Tributyl Phosphate

“…We circumvented this issue in the following way: (i) MC simulations were performed with the MPW1K functional which is known to yield higher barriers and (ii) TDDFT calculations were performed with the B3LYP functional on the sublist of MC configurations with conveniently modified geometries. This methodology has been proven to be very efficient for metastable (LiClO 4 ) n – oligomers. , For stable and for metastable systems with high dissociation barriers, we have used the B3LYP functional throughout the procedure. The basis set dependence has been investigated on the first triplet state of the trimethyl phosphate (TMP) system, where both the small pSDD and the large aug-cc-pvdz basis sets can be used for the MC simulation. It can be seen in Figure S1 that using the large basis provokes a shift in the low energy band of the spectrum toward larger wavelengths, as large as 70 nm.…”

“…We circumvented this issue in the following way: (i) MC simulations were performed with the MPW1K functional which is known to yield higher barriers and (ii) TDDFT calculations were performed with the B3LYP functional on the sublist of MC configurations with conveniently modified geometries. This methodology has been proven to be very efficient for metastable (LiClO 4 ) n – oligomers. , For stable and for metastable systems with high dissociation barriers, we have used the B3LYP functional throughout the procedure.…”

“…This methodology has been proven to be very efficient for metastable (LiClO 4 ) n − oligomers. 24,25 For stable and for metastable systems with high dissociation barriers, we have used the B3LYP functional throughout the procedure.…”