Molecular Dynamics and ab Initio Studies of the Effects of Substituent Groups on the Thermodynamic Properties and Structure of Four Selected Imidazolium-Based [Tf₂N^–] Ionic Liquids

Abstract

All-atom molecular dynamics simulations combined with ab initio calculations are used to study the thermodynamic properties and microscopic structure of four ionic liquids (ILs) based on the imidazolium cation with different alkyl side branches, ([bmmim] + , 1-butyl-2,3-dimethylimidazolium; [bmim] + , 1-butyl-3-methylimidazolium; [apmim] + , 1-(3-aminopropyl)-3-methylimidazolium; [mim] + , 1-methylimidazolium), paired with the [(CF 3 SO 2 ) 2 N] − , bis-(trifluoromethanesulfonyl)imide anion, in the temperature range of (298 to 600) K. We observed the highest value of the molar internal energy, enthalpy of vaporization, and cohesive energy density for the amine-functionalized [apmim][Tf 2 N] ionic liquid. Structural analysis shows that the amine functionalization of the end of the alkyl side chain of imidazolium cation does not significantly affect the organization of [Tf 2 N] − around [apmim] + , but additional NH 2 groups lead to short-range cation−cation structural correlations between neighboring [apmim] + . The C2 methylation extensively affects preferential out-of-plane face-toface locations of [Tf 2 N] − around [bmmim] + and also the cation−cation distributions. [mim][Tf 2 N] has the highest simulated density and better packing efficiency of liquid phase in comparison with other studied ILs. The strongest first shell probability density region of [mim] + neighbors above and below the imidazolium ring of the reference cation represents better π−π stacking in the liquid phase of this ionic liquid. The presented results determine the role of the cation structure on the properties of this family of ILs. Good agreement was achieved between simulation results of the bulk phase and quantum calculations which are performed to determine the optimized structure of isolated ion pairs in chosen configurations and the strength of cation−anion interactions.

The Relationship between the Structure and Properties of Amino Acid Ionic Liquids

“…H-bonding is also a factor affecting the viscosities of ILs. Compounds with fewer hydrogen bonds have a lower viscosity [46]. In our case, fewer hydrogen bonds in ammonium AAILs do not decrease their viscosity relative to the imidazolium AAILs, which is associated with conjugated cation structure.…”

Viscosity, Conductivity, and Electrochemical Property of Dicyanamide Ionic Liquids

“…Hydrogen bonding is an important factor affected the viscosity of ILs. Fewer hydrogen bonds may lead to lower viscosity of IL (Kowsari et al, 2014 ). However, the DCA IL [C 4 mim][N(CN) 2 ] with active hydrogen on C(2) exhibits lower viscosity than [C 4 m 2 im][N(CN) 2 ].…”

Tracing Dynamics, Self-Diffusion, and Nanoscale Structural Heterogeneity of Pure and Binary Mixtures of Ionic Liquid 1-Hexyl-2,3-dimethylimidazolium Bis(fluorosulfonyl)imide with Acetonitrile: Insights from Molecular Dynamics Simulations

“…According to structural studies of the 1-alkyl-3-methylimidazolium ILs based on [TFSI] − , the strongest structural correlations between [TFSI] − and the imidazolium cations are related to the interactions between the oxygen atoms of the anions and the hydrogen atom on the C R atom of the imidazolium ring. 61,79 In this work, a similar correlation was investigated between the cation and anion in the novel C2methylated IL [C 6 mmim][FSI] based on the partial site−site RDF analysis (Figure 7a). A more detailed structural analysis of IL [C 6 mmim][FSI]/ACN mixtures was also carried out by calculating the RDFs between selected atomic sites of the IL and ACN.…”