The potential applications of ionic liquids and related analogues are diverse. However, for large-­scale
industrial applications low cost ionic liquids are required. Moreover, for the full potential of ionic liquids
to be realised, a fundamental link between molecular level interactions, structuring and the bulk phase
properties must be established.
Deep eutectic solvents (DESs) and protic ionic liquids have been identified as candidates for
the potential application of chalcopyrite leaching. The choline chloride – urea DES and 1-­
butylimidazolium hydrogensulphate protic ionic liquid were selected as systems of primary interest.
Local structuring within the selected systems has been investigated, with an emphasis on the
hydrogen bonding interactions.
The choline chloride – urea mixture is a prototypical example of a DES. Using DFT, the
pairwise interactions between the constituent components, and within clusters composed of
n.urea.choline-­chloride (n = 1-­3), have been evaluated. Many different types of hydrogen bond have
been identified, exhibiting flexibility in both strength and number. The formation of the commonly
proposed [2urea⋅Cl]– complexed anion has been scrutinised and found to be energetically competitive
with other interactions. Moreover, contrary to existing proposals, the negative charge is found to
remain localised on chloride.
The cation-­anion and anion-­anion interactions within [C4Him][HSO4] and related systems have
been compared and contrasted;; ion pairs were evaluated using DFT and the bulk systems modelled
using classical MD. Local structuring within [C4Him][HSO4] exhibits features of both the aprotic
analogue and alkylammonium protic ionic liquids. [HSO4]–⋅⋅⋅[HSO4]– interactions have been
considered and found to be a notable feature of the [HSO4]– ionic liquids studied. It is anticipated that
the formation of [HSO4]– aggregates influences the properties of the bulk systems.
A QM/MM method for the study of ionic liquids is introduced. Preliminary analysis suggests
that this is a viable approach for the investigation of local structuring within ionic liquids.