The local structure in the BmimPF6/acetonitrile mixture: the charge distribution effect

摘要: The changes of the local structure in binary mixture 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6) ionic liquid and acetonitrile are investigated over entire composition range. Two charge distribution models ions considered: first one, atomic fractional charges cations anions kept equal with those neat liquid, hence they independent from mole fraction while second one is scaled up by a dependent factor. sum these converge to +1e -1e on cation anion, respectively, at infinite dilution. All other interactions geometry parameters (i.e., Lennard-Jones, bond stretching, angle bending dihedral parameters) identical two cases. effect hydrogen bonding between counterions themselves solvent molecules, as well stacking cations, analyzed. To this end, distances, characteristic formed donor moiety its nearest neighbor acceptor, coordinate system that defines unambiguously orientation reference neighbor, introduced. It shown that, variable model, neighboring cation-anion pairs maintain their relative arrangement similar down an xIL = 0.10, whereas case constant model such occur already 0.20. Furthermore, analysis distance distributions anion around indicates range, there different preferred arrangements cations. In similarly forms distorted cation, located farther forming no it. population types found be sensitive further decrease fraction. These findings correlate experimental results concerning behavior many physical chemical properties (e.g., excess volume, viscosity, shift, infrared Raman vibrational mode shifts, diffusion, etc.) were undergo drastic change Our show range transition occurs situation where macroscopic determined primarily solvation molecular solvent.