FTIR and DFT studies of LiTFSI solvation in 3-methyl-2-oxazolidinone

• Implicitly and explicitly interacting NMO solvent molecules are distinguished.
• Predicted vibrational modes of computed NMO species agree with experimental results.
• Averaged solvation number of Li+ in NMO is 4.

Combined computational/FTIR spectroscopic analyses of 3-methyl-2-oxazolidinone (NMO) solutions with varying molar ratios of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are reported. Based on the second derivative spectral profile, overlapping peaks are distinguished as well as assigned to the vibrational modes of implicitly and explicitly interacting NMO molecules. Thereby, the geometry of a monomeric, a dimeric and a simplified solvation structure [Li(NMO)1]+ are optimized with a polarizable continuum model at a B3LYP theoretical level. With increasing contents of LiTFSI, the formation of Li+ solvation structures is scrutinized by semi-quantitative analysis of deconvoluted integral peak areas for three different ring-related vibrations and CO-stretch vibration. A discrepancy in the obtained data is observed implying the influence of the TFSI anion the ring-related vibrations are prone to. The solvation number of 4 is determined according to the CO-signal in diluted solution, which is proven by the computed Gibbs free energy for solvation of [Li(NMO)4]+ in a NMO medium (− 41.7 kcal mol− 1).

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