Ricerc@Sapienza

We explore the structure of two ionic liquids based on the choline cation and the monoanion
of the maleic acid. We consider two isomers of the anion (H-maleate, the cis-isomer and H-fumarate,
the trans-isomer) having different physical chemical properties. H-maleate assumes a closed structure
and forms a strong intramolecular hydrogen bond whereas H-fumarate has an open structure.
X-ray diffraction, infrared and Raman spectroscopy and molecular dynamics have been used
to provide a reliable picture of the interactions which characterize the structure of the fluids.
All calculations indicate that the choline cation prefers to connect mainly to the carboxylate group
through OH· · ·O interactions in both the compounds and orient the charged head N(CH3
)
+
3
toward
the negative portion of the anion. However, the different structure of the two anions affects the
distribution of the ionic components in the fluid. The trans conformation of H-fumarate allows further
interactions between anions through COOH and CO –
2 groups whereas intramolecular hydrogen
bonding in H-maleate prevents this association. Our theoretical findings have been validated by
comparing them with experimental X-ray data and infrared and Raman spectra.