Structure of ethylammonium hydrogen sulfate protic ionic liquid through DFT calculations and MD simulations: the role of hydrogen bonds

Understanding how structure and interactions between ions affect physicochemical properties is of great importance for the rational design, synthesis, and applications of new “target-specific” ionic liquids. Motivated by this need, in this paper, we present the results of density functional theory (DFT) studies of few small clusters including up to six ion pairs and molecular dynamics (MD) simulations of the bulk phase of ethylammonium hydrogen sulfate (EA/SA) protic ionic liquid. Special attention is being focused here on hydrogen bond properties and their role in the structure formation of ionic liquid. By using the DFT calculations, it was shown that an increase of the cluster size leads to a networked structure with as many as possible cation–anion hydrogen bonds, but these bonds are distorted. Similar results were obtained also through MD simulations of the bulk phase of the EA/SA. In addition, in the simulated liquid, the formation of anion–anion hydrogen bonds also is possible. On the basis of our calculations together with the literature data, a relationship between the structure and physicochemical properties of the EA/SA liquid was established.