Criteria for solvate ionic liquids.

Certain concentrated mixtures of salts and solvents are not simply "solutions" anymore, but they may be described as "ionic liquids". In this perspective paper, we describe possible criteria for the new family of ionic liquids: "solvate" ionic liquids. This subclass of ionic liquids was originally proposed by Angell et al. in their recent review; however, their criteria remain to be debated. Concentrated mixtures of lithium salts and organic solvents are useful models for these solvate ionic liquids, and the effects of the salt concentration, types of solvents, and counter anions of the lithium salts on their structure and properties have been explored to enable contrast with traditional solutions, and to help determine whether a given mixture belongs to the solvate ionic liquid or not.