Abstract
The results of densimetry investigation of the solutions of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4), hexafluorophosphate (BMIMPF6) and bromide (BMIMBr) in propylene carbonate (PC) at 298.15, 318.15, 338.15 and 358.15 К are presented and discussed in terms of apparent partial molar volumes and solvation contribution. Density measurements were carried out using the vibrational tube densitometer Mettler Toledo DM 50 with accuracy ± 3∙10-5 g/cm3. The limiting partial molar volumes of investigated ionic liquids in PC were obtained from density experiment using Masson equation and divided into ionic contributions. Limiting partial molar volumes of BMIMBF4, BMIMPF6 and BMIMBr in PC slightly increase with the increase of temperature. The limiting partial molar volumes of BMIM+ cation obtained from three ionic liquids with different anions was found to have the same value, 115 cm3/mol at 298.15 K. The intrinsic volume of BMIM+ cation estimated from quantum chemical calculations at the M062X/6‑311++G(d,p) theory level exceeds one obtained from density experiment indicating that solvation of cation has a negative contribution to the volume of ion in propylene carbonate. In order to investigate the microscopic structure of the BMIM+ solvation shell in PC, molecular dynamics simulation of the infinitely dilute solution was carried out in the NVT ensemble at 298.15 K. The results of the simulation reveal that 5-6 PC molecules forming the first solvation shell penetrate into the inner space of the cation, which agrees with the results of a density experiment treatment. From the analysis of the cation-solvent site-site radial distribution functions and the running coordination numbers it was established that the most probable coordination center of PC molecule is carbonyl oxygen.
Highlights
The room temperature ionic liquids (RTILs) due to their ionic structure and liquid state at room temperature have a plenty of specific features such as negligible vapor pressure, non-flammability, broad range of liquid state, high thermal stability, high solvating capacity and wide electrochemical window [1]
Mixtures of RTILs with aprotic solvents like propylene carbonate are widely used in lithium-ion batteries [7], super capacitors [8] and solar cells [9] due to lower viscosity and higher ion mobility
The microscopic structure of the first solvation shell of 1-butyl-3-methylimidazolium in propylene carbonate at infinite dilution was studied by means of molecular dynamics simulation
Summary
The room temperature ionic liquids (RTILs) due to their ionic structure and liquid state at room temperature have a plenty of specific features such as negligible vapor pressure, non-flammability, broad range of liquid state, high thermal stability, high solvating capacity and wide electrochemical window [1]. It seems appropriate to use a combination of experimental and computing methods for examination of solvation structure in such complicated systems like mixtures of RTILs with aprotic solvents. Density and solvation effects of imidazolium based ionic liquids in propylene carbonate. Methylimidazolium tetrafluoroborate (BMIMBF4), hexafluorophosphate (BMIMPF6) and bromide (BMIMBr) with propylene carbonate (PC) was measured with high accuracy in the temperature range. The microscopic structure of the first solvation shell of 1-butyl-3-methylimidazolium in propylene carbonate at infinite dilution was studied by means of molecular dynamics simulation. 1-Butyl-3-methylimidazolium bromide was dried under reduced pressure in water bath at 85 oC for 4-5 hours using rotary evaporator and recrystallized using liquid nitrogen. A set of 10 solutions for each RTIL+PC systems in the range of concentrations from 5·10-3 to 1·10-1 mol/dm were used for the density measurements. The calibration of densitometer was made using ultra-pure water and air at atmospheric pressure and 293.15 K
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