Solvation of AgTFSI in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid investigated by vibrational spectroscopy and DFT calculations

In this paper we investigate the solvation of silver bis(trifluoromethylsulfonyl)imide salt (AgTFSI) in 1-ethyl-3-methylimidazolium TFSI [EMI][TFSI] ionic liquid by combining Raman and infrared (IR) spectroscopies with density functional theory (DFT) calculations. The IR and Raman spectra were measured in the 200-4000cm(-1) spectral region for AgTFSI/[EMI][TFSI] solutions with different concentrations ([AgTFSI] <0.2 mole fraction). The analysis of the spectra shows that the spectral features observed by dissolution of AgTFSI in [EMI][TFSI] solution originate from interactions between the Ag+ cation and the first neighboring TFSI anions to form relatively stable Ag complexes. The gas phase' interaction energy of a type [Ag(TFSI)(3)](2-) complex was evaluated by DFT calculations and compared with other interionic interaction energy contributions. The predicted spectral signatures because of the [Ag(TFSI)(3)](2-) complex were assessed in order to interpret the main IR and Raman spectral features observed. The formation of such complexes leads to the appearance of new interaction-induced bands situated at 753cm(-1) in Raman and at 1015 and 1371cm(-1) in IR, respectively. These specific spectral signatures are associated with the breathing' mode and the S-N-S and S-O stretching modes of the TFSI anions engaged in the complex. Finally, all these findings are discussed in terms of interaction mechanisms enabling the electrodeposition characteristics of silver from AgTFSI/[EMI][TFSI] IL-based electrolytic solutions. Copyright (c) 2015 John Wiley & Sons, Ltd.