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. 2024 Nov 14;29(22):5377.
doi: 10.3390/molecules29225377.

Vibrational Spectroscopic Identification of the [AlCl2]+ Cation in Ether-Containing Liquid Electrolytes

Gabriela P Gomide  1 , Wagner A Alves  1 , Andrzej Eilmes  2
Affiliations

Vibrational Spectroscopic Identification of the [AlCl2]+ Cation in Ether-Containing Liquid Electrolytes

Gabriela P Gomide et al. Molecules. .

Abstract

A Raman and IR study of AlCl3-based ethereal solutions is here presented and aims at identifying the [AlCl2]+ cation, which has been so far unambiguously characterized by 27Al NMR spectrometry. To do that, experimental-theoretical vibrational spectroscopy was so employed, and the data are interpreted successfully. As a known amount of water is added to the tetrahydrofuran (THF)-containing electrolyte, a Raman band at 271 cm-1 has its intensity increased along with the most intense band of [AlCl4]-, and such behavior is also seen for a band at 405 cm-1 in the IR spectra. New bands at around 420 and 400 cm-1 are observed in both Raman and IR spectra for the tetraglyme (G4)-based systems. The [AlCl2(THF)4]+ complex, in the cis and trans forms, is present in the cyclic ether, while the cis-[AlCl2(G4)]+ isomer is identified in the acyclic one.

Keywords: aluminum chloride; ethereal liquid electrolytes; vibrational spectroscopy.

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Conflict of interest statement

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Raman spectra of a 0.5 mol kg−1 AlCl3 solution at the region of the νAlO and νAlCl vibrations: (a) AlCl3-THF system; (b) AlCl3-THF:H2O system with water/salt molar ratio of 0.4.
Figure 2
Figure 2
Far-IR spectra of a 0.5 mol kg−1 AlCl3 solution at the region of the νAlO and νAlCl modes: (a) AlCl3-THF system; (b) AlCl3-THF:H2O system with water/salt molar ratio equal to 0.4.
Figure 3
Figure 3
Raman spectra of AlCl3/G4 solutions at the region of the νAlO and νAlCl vibrations: (a) 1 mol kg−1; (b) 2 mol kg−1.
Figure 4
Figure 4
Far-IR spectra of AlCl3/G4 solutions at the region of the νAlO and νAlCl vibrations: (a) 1 mol kg−1; (b) 2 mol kg−1.
Figure 5
Figure 5
AIMD-simulated Raman (a) and IR (b) spectra of AlCln complexes with explicit THF solvent molecules.
Figure 6
Figure 6
AIMD-simulated Raman (a) and IR (b) spectra of AlCln complexes with explicit G4 solvent molecule.
Figure 7
Figure 7
Calculated harmonic (a) and anharmonic (b) Raman spectrum of the [AlCl4]− anion.
See this image and copyright information in PMC

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