However, the possibility of almost free adaptation of the structure of ILs to obtain the desired properties ("designability")-including toxicity-and the related multiplicity of their potential applications in various industries remain unquestionable advantages. As a result of the development of specific models on the basis of collected experimental data, methods based on machine learning are now becoming helpful for achieving favorable results and predicting the properties of designed ILs. However, the desired effects can be achieved not only by selecting the right combination of cation and anion or by slight structural modifications to one of the ions (e.g., altering the length of an alkyl chain) but also by creating entirely new ionic systems by mixing two or more ILs. Such an approach offers an additional degree of freedom in the choice of cation and anion and does not require the design of a new synthesis process (as in the case of anion exchange or other structural modifications), and the resulting IL mixtures with potentially nonideal characteristics can have new and unique properties that none of the constituent ionic liquids possess . To distinguish such systems from simple mixtures, the name double salt ionic liquids (DSILs) has been proposed . Analogous to deep eutectic solvents (DESs), numerous properties of DSILs result from chemical interactions between the constituent ions, and a change in the molar ratio of the parent ILs can result in a significant change in the properties of a given system , which justifies the investigation of the physical, physicochemical and biological properties of various DSIL systems. Moreover, in some cases, DSILs can become the basis for new DESs .