Computational NMR Spectroscopy of Ionic Liquids: [C₄C₁im]Cl/Water Mixtures

In this work, I have analyzed the structure of binary mixtures of 1-butyl-3-methylimidazolium chloride ionic liquid, [C₄C₁im]Cl, and water, using computational NMR spectroscopy. The structure of the complex fluid phase, where the ionic and hydrophobic nature of ionic liquids is further complicated by the addition of water, is first generated by classical Molecular Dynamics (MD) and then validated by calculating the NMR properties with DFT at the ONIOM(B3LYP/cc-pVTZ//B3LYP/3-21G) on clusters extracted during the MD trajectories. Three ionic liquid/water mixtures have been considered with the [C₄C₁im]Cl mole fraction of 1.00, 0.50, and 0.01, that is the pure ionic liquid [C₄C₁im]Cl, the equimolar [C₄C₁im]Cl/water mixture, and a diluted solution of [C₄C₁im]Cl in water. A good agreement is obtained with published experimental data that, at the same time, validates the structural features obtained from the MD and the force field used, and provides an example of the power of NMR spectroscopy applied to complex fluid phases.