Microscopic solvation environments in a prototype room-temperature ionic liquid as elucidated by resonance Raman spectroscopy of iodine and bromine

Abstract

Microscopic solvation environments in a prototype ionic liquid, bmimTf(2)N; 1-buty1-3-methyl-imidazoliumbis(trifluoromethanesulfonyl)imide, have been studied with the use of halides, X-2 and X-n(-) (X = I, Br; n = 3,5), as molecular probes. Resonance Raman spectroscopy has been used to detect these halogen species existing in bmimTf(2)N as well as in reference solvents including heptane, cyclohexane, KX/H2O and benzene. In heptane and cyclohexane, only free X-2 species are detected. In KX/H2O, only X-n(-) and, in benzene, only benzene-X-2 complexes are detected. On the contrary, free X-2 and X-n(-) are concomitantly detected in bmimTf(2)N, indicating that there are two distinct solvation environments in bmimTf(2)N, non-polar environments that solvate free X-2 and polar environments that stabilize X-n(-) These two distinct solvation environments are most likely to arise from microscopic structural heterogeneity of ionic liquids. (C) 2016 Elsevier B.V. All rights reserved.