Theoretical Studies On The Structure Of The Functionalied Ionic Liquids

In this work, the structures and properties of the basic ionic liquid [Emim]OH and four -SO3H functionalized acidic ionic liquids were studied by DFT methods.The structure of ionic liquid [Emim]OH and the effect of water molecules on this ionic liquid were studied by DFT theory. It was found that the cation and the anion could not exist as the form of ion pairs in [Emim]OH, the most stable structure of [Emim]OH was the complex of one water molecule and imidazole carbene. Further studies showed that the water molecules mainly had effect on the anion: they could disperse the negative charge of O atom at OH- and form hydroxide ion-water clusters with OH-. When there were two water molecules in the ionic liquid [Emim]OH, the ion pair of anionic cluster OH-(H2O)2 and imidazole cation which was connected by hydrogen bonded networks generated. The configurations formed near C2-H fragment of imidazole were favored and the hydrogen bonding interaction played an important role in these complexes.The precursor compound (zwitterion), cation and the ion pairs of four -SO3H functionalized acidic ionic liquids were studied systematically by DFT theory. The calculation results indicated that a great tendency to form strong intramolecular hydrogen bonds was present in the zwitterion, and this tendency was weakened in the cations that were the protonation product of zwitterions. In the ion pairs, the intermolecular hydrogen bonds were the primary, and the intramolecular hydrogen bonds were weakened to a certain extent. The strongest interaction in these ionic liquids was found between the anion and the functional group. Further study of the natural bond orbital charge population analysis showed that the hydrogen bond interactions made the net charge on the hydrogen bonded H atoms increased, but there were no direct relation between the total charge transfer and the stability of the ionic liquid system.