Quantum chemical studies on nanostructures of the hydrated methylimidazolium-based ionic liquids

The B3LYP and M06-2X suits of density functional theory in conjunction with the 6-311++G(2d,2p) basis set were employed to investigate the nanostructures formed from the interaction between water molecules and ionic liquids based on methylimidazolium cation (MIM+) with the anions (X1-5=CH3COO-, CF3COO-, NO3-, BF4-, and N(CN)(2)(-)) on a molecular level. Based on the calculated Gibbs free binding energies, the predicted stability order of nanostructures in the gas phase is [MIM]X-1 > [MIM]X-2 > [MIM]X-3 > [MIM]X-4 > [MIM]X-5. The estimated solvation enthalpy of ions implied that the stability of anions NO3- and CH3COO- in water is greater than those of MIM+ and other anions. Tendency of hydrated anions to react with hydrated cations to form the solvated ion pairs is slightly smaller than the tendency of hydrated anions (cations) to react with unsolvated cations (anions). The strengths of the interactions in studied categories follow the trend X-W > MIM-W > [MIM]X - W.