Probing electron density of H-bonding between cation-anion of imidazolium-based ionic liquids with different anions by vibrational spectroscopy.
Attenuated total reflection infrared spectroscopy and density functional theory calculation have been employed to study the spectral properties of imidazolium-based ionic liquids (ILs) with different anions. ILs based on 1-butyl-3-methylimidazolium cation with different anions, OH(-), CF(3)CO(2)(-), HSO(4)(-), H(2)PO(4)(-), Cl(-), PF(6)(-), and BF(4)(-), are investigated in the present work. It has been shown that the C(2)-H stretching vibration of the imidazolium ring is closely related to the electron density of H-bonding between the two closest cations and anions for pure ILs. The electron density of H-bonding between cation and anion with different anions decreases in the order [OH](-) > [H(2)PO(4)](-) > [HSO(4)](-) > [CF(3)CO(2)](-) > [Cl](-) > [BF(4)](-) > [PF(6)](-). For aqueous ILs, with increasing water content, the aromatic C-H stretching vibration of the imidazolium cation showed systematic blue-shifts. Especially for BmimOH, the nu(C(2))(-H) undergoes a drastic blue-shift by 58 cm(-1), suggesting that the formation of the strong hydrogen bonds O-H...O may greatly weaken the electron density of H-bonding between the cation and anion of ILs.
Gao
Yan
Y
Department of Chemistry, Zhejiang University, Hangzhou 310027, PR China.
Zhang
Liqun
L
Wang
Yong
Y
Li
Haoran
H
D000838:Anions / Q000737:chemistry; D002412:Cations / Q000737:chemistry; D003198:Computer Simulation; D004583:Electrons; D006860:Hydrogen Bonding; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D008956:Models, Chemical
C525963:1-butyl-3-methylimidazolium; D000838:Anions; D002412:Cations; D007093:Imidazoles; D052578:Ionic Liquids