Tuning of the freezing and melting points of [Hmim][NO3] by the addition of water and nitrate salts

Abstract

The fact that the physical and chemical properties of ionic liquids can be tailored is one of their key features. In most cases this is achieved by the appropriate selection of the cation and anion pair. In this paper we suggest that simple chemometric models can be used to describe various properties of these salts. We chose water and metal ions, generally considered as contaminants, to tune the melting and freezing points of a model ionic liquid, 1-methyl-imidazolium nitrate ([Hmim][NO₃]). Principal component analysis was used to select two representative metal ions (Li(I) and Cu(II)) on the basis of the charge and atomic radius of the cation, the crystallization water and the melting point of the nitrate salt, which we believed would affect the behaviour of the [Hmim][NO₃]. A D-optimal design was used to plan the best experiments to obtain empirical models capable of predicting the melting and freezing points of this ionic liquid as a function of water and metal cation content.