Deep eutectic solvents: a structural point of view on the role of the anion

The structural properties of four deep eutectic solvents (DESs), namely a 1:2 mixture of choline chloride and urea, and three analogous DESs containing different anions in place of chloride, namely fluoride, nitrate or acetate, were investigated by using Molecular Dynamics. The order of the DES melting points was found not to correlate with the strength of urea-anion hydrogen bonds. However, the DES low melting points are related to the anion ability to build favourable networks of interactions with both choline and urea, in such a way as to maximize the hydrogen bonds among all the different moieties of the system.