Effect of structure and interaction on physicochemical properties of new [Emim][BF3X] complex anion ionic liquids studied by quantum chemistry

Abstract One of the key challenges in the industrial application of ionic liquids (ILs) is their extreme characteristics, such as viscosity, glass-transition temperatures and conductivity. Understanding the relationship between ILs structure and physicochemical propertie is a crucial aspect of the directed design of ILs with good properties, which is a prerequisite for their successful implementation in industrial processes. In this work, high-level quantum-chemical research for four pairs ionic liquids, [Emim][X] and [Emim][BF3X] (X=CH3SO3, EtSO4, HSO4, Tos), was performed, to provide a new insight into the property variances at the molecular level. The result shows that the overall stability of ionic liquids is contributed with hydrogen bonding network between the protons in the C-H and N-H of the cation and oxygen atoms of the anion, as well as fluorine atoms. The nature and strength of the interionic interaction were measured via atoms in molecules analysis and sobEDAw method and results suggested that BF3 could waning interionic interaction of ion pairs. Moreover, a close relation between the binding energies of ion pairs and physicochemical properties was established: the weaker the interionic interaction, the lower is the viscosity and glass-transition, and the higher is the conductivity.