Vibrational assignments, conformational analysis, and molecular structures of CnmimNTF2 (n = 2, 4, 6, and 8) imidazolium-based ionic liquids: a combined experimental and quantum chemical approach

This work is aimed at providing physical insights about the interactions of cations, anion, and ion pairs of four imidazolium-based ionic liquids of C n mim NTF 2 with varying alkyl chain lengths ( n  = 2, 4, 6, and 8) using both DFT calculations and vibrational spectroscopic measurements (IR absorp...

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Bibliographic Details
Published in:Journal of the Iranian Chemical Society 2017, Vol.14 (6), p.1281-1300
Main Authors: Azizi-Toupkanloo, Hossein, Tayyari, Sayyed Faramarz, Nancarrow, Paul
Format: Article
Language:English
Subjects:
Analytical Chemistry
Biochemistry
Chemistry
Chemistry and Materials Science
Inorganic Chemistry
Organic Chemistry
Original Paper
Physical Chemistry
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Summary:This work is aimed at providing physical insights about the interactions of cations, anion, and ion pairs of four imidazolium-based ionic liquids of C n mim NTF 2 with varying alkyl chain lengths ( n  = 2, 4, 6, and 8) using both DFT calculations and vibrational spectroscopic measurements (IR absorption and Raman scattering) in the mid- and far regions. The calculated Mulliken charge distributions of C n mim NTF 2 ion pairs indicate that hydrogen-bonding interactions between oxygen and nitrogen atoms (more negative charge) on NTF 2 - anion and the hydrogen atoms (more positive charge) on the imidazolium ring play a dominating role in the formation of ion pair. Thirteen stable conformers of C 2 mim NTF 2 were optimized. According to our results, the strongest and weakest hydrogen bonds were existing in C 2 mim NTF 2 and C 8 mim NTF 2 , respectively. A redshift of 290, 262, 258, and 257 cm −1 has been observed for cations involving C 2 mim + , C 4 mim + , C 6 mim + , and stretching vibrations of C 12 - H 3 , respectively. By increasing the chain length, the strength of hydrogen bonds decreases as a result of C 12 - H 3 bond elongation and less changes are observed in stretching vibrations of C 12 - H 3 compared to the free cations. To the best of our knowledge, this research is the first work which reports the far-IR of C 4 mim NTF 2 , C 6 mim NTF 2 , and C 8 mim NTF 2 and the mid-IR of C 8 mim NTF 2 .
ISSN:1735-207X
1735-2428
DOI:10.1007/s13738-017-1079-z