Fused salts, ionic liquid structure

To this end, we review the physics of high temperature fused salts and draw on observations made in these systems to understand the microscopic structure of ionic liquids. We also review some physics of glass-forming liquids, focusing on concepts necessary to understand structural and dynamic inhomogeneity in ILs. We provide a broad review of attempts to characterize ILs empirically, and discuss those results with reference to simulation and theoretical studies. The overall objective of this study is to develop a conceptual toolbox that can be used to interpret experimental results in ILs and help identify useful new questions for the field. To this end, we present a series of principles describing the nature of solvation in ionic liquids at the conclusion of this chapter. 

This discussion of the structure and dynamics of fused salts provides only the briefest overview of their properties. However, even this minimal background will prove a useful reference point as we turn our attention to room temperature ionic liquids. 

Bloom H., Bockris J. O M., Structural Aspects of Ionic Liquids in Fused Salts, B. R. Sundheim, ed., McGraw-Hill, New York, 1964, p. 1. 

From the standpoint of this comparison (Fig. 5.54), it is seen that the concept of a complex ion in a molten salt is at least as tenable as that of an ion with a primary solvation sheath (Section 2.4) in aqueous solutions. Whatexperimental evidence exists for complex ions in fused salt mixtures To anwer this question, one must discuss some results of investigating the structure of mixtures of simple ionic liquids. 

It has just been argued that the conductivities of simple ionic liquids, on the one hand, and liquid sihca and water, on the other, are vastly different because a fused salt is an unassociated liquid (it consists of individual particles) whereas both molten silica and water are associated liquids with network structures. What is the situation with regard to the viscosities of fused salts, water, and fused silica Experiments indicate that whereas water and fused NaCl have similar viscosities not far above the melting points of ice and solid salt, respectively, fused silica is a highly viscous liquid (Table 5.46). Here then is an interesting problem. 

Then what are the ionic liquids In people s usual opinions, the salts that consist of organic cations and inorganic or organic anions, in the form of liquid at or around the ambient temperature, are called usually the room-temperature ionic liquid (RTIL), the ambient-temperature ionic liquid (ATIL), or the room-temperature molten salts (RTMS), the room-temperature fused salts (RTFS), and can be called the ionic liquid (IL) for abbreviation. The feature of ionic liquids being liquid at the room temperature is attributed to the asymmetric structures of the ionic liquids with big difference in volume of anions and cations leading to little electrostatic attraction. 

More interest has been shown in ionic liquids derived from the 5- and 6-membered saturated nitrogen heterocycles, pyrrolidine and piperidine. iV,lV-dialkyl salts from these secondary amines display polymorphism f Section 11.2.31 as well as a propensity to frustrate attenpts to crystallise them Related materials (with some ring unsaturation, two heteroatoms or wiA fused ring structures) are discussed in Section 11.19.S. 

---