Toward understanding the structural heterogeneity and ion pair stability in dicationic ionic liquids

Abstract

The structural and dynamical properties of dicationic ionic liquids (DILs) [Cn(mim)2](Tf2N)2, that is, 3-methylimidazolium dications separated by an alkyl chain and with bis(trifluoromethylsulfonyl)amide as the anion, were investigated by molecular dynamics (MD) simulation in combination with small/wide-angle X-ray scattering (SWAXS) measurements. Enhanced spatial heterogeneity is observed as the DIL chain length is increased, characterized by the changes in the scattering and the increased heterogeneity order parameter (HOP). Temperature variation imposes only slight influences on the local structures of DILs compared to monocationic ionic liquids (MILs). The peaks at 0.9 Å(-1) and 1.4 Å(-1) of the structure function shift towards low Q as the temperature increases, in a similar manner to MILs, and changes in peak positions in response to temperature changes are reflected in HOP variations. However, the prepeak shift with increasing temperature is ∼3 times smaller in DILs compared to MILs, and both MD and SWAXS indicate a DIL-specific prepeak shifting. Furthermore, the high ion pair/ion cage stability in DILs is indicative of high thermal stability and relative insensitivity of structural heterogeneity to temperature variation, which might be caused by the stronger Coulombic interactions in DILs.

Understanding the hydrogen bonds in ionic liquids and their roles in properties and reactions

“…[1][2][3] Each breakthrough, such as dissolving cellulose, 4 a liquid mirror in a space telescope, 5,6 and a catalyst in CO 2 electro-reduction, 7 is rich in new technology. Since air-stable ILs containing the anions [PF 6 ] À , [BF 4 ] À , and [NTf 2 ] À were reported in the 1990s, 8,9 RTILs have been applied in various fields, such as CO 2 capture, [10][11][12][13] extraction/separation, [14][15][16] synthesis and catalytic reactions, 2 electrochemistry and metallurgy, [17][18][19][20][21] soft materials, [22][23][24] and biosystems 25,26 and some results were quite encouraging. Recent developments have prompted the use of ILs in confined environments, such as carbon nanotubes and graphene, leading to many new applications.…”

Homogeneous capture and heterogeneous separation of proteins by PEG-functionalized ionic liquid–water systems

“…The (CH 2 CH 2 O) n segments of PEG chains of the ILs are probably prefer to interact with the ammonium cation (-NH 3 + ) instead of anion (-COO À ) of Cyt.c by favourable hydrogen bonding and ion-dipole interactions, which allows the transfer of protein into the IL phase. In addition, considering the fact that the PEG-functionalized ILs used in this study include dications and exhibit a distinctive electrical double layer at the electrode surface, 43,44 the stronger columbic interaction between the imidazolium cation and protein is another possible driving force for the extraction of Cyt.c.…”

Validation of Structural Grounds for Anomalous Molecular Mobility in Ionic Liquid Glasses

“…The most unusual characteristic of ILs is their nanoscale self-organization, leading to the formation of heterogeneities [ 28 , 29 ]. There are plenty of theoretical investigations regarding the effects of molecular self-organization in bulk ILs [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ]. It was experimentally proven that charged cationic head groups and anions tend to aggregate in polar nanodomains, and hydrophobic alkyl chains form apolar nanodomains.…”