Computational studies of the structure and cation-anion interactions in 1-ethyl-3-methylimidazolium lactate ionic liquid

• Published in: Science China. Chemistry 2012-08, Vol.55 (8), p.1548-1556
• Main Authors: He, HongYan, Zheng, YanZhen, Chen, Hui, Zhang, XiaoChun, Yao, XiaoQian, Zhang, SuoJiang
• Format: Article
• Language: English
• Subjects: Anions; Carbonyls; Cations; Chemical bonds; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Doppler effect; Elongation; Ion pairs; Ionic liquids; Mathematical analysis; Quantum chemistry; Red shift; 乙基; 乳酸盐; 甲基咪唑; 离子液体; 离子相互作用; 量子化学计算; 阳离子; 阴离子
• ISSN: 1674-7291; 1869-1870
• DOI: 10.1007/s11426-012-4649-z

Quantum chemical calculations of the structures and cation-anion interaction of 1-ethyl-3-methylimidazolium lactate （[Em- im][LAC]） ion pair at the B3LYP/6-31＋＋G＊＊ theoretical level were performed. The relevant geometrical characteristics, en- ergy properties, intermolecular H-bonds （H-bonds）, and calculated IR vibrations with respect to isolated ions were systemati- cally discussed. The natural bond orbital （NBO） and atoms in molecule （AIM） analyses were also employed to understand the nature of the interactions between cation and anion. The five most stable geometries were verified by analyzing the relative energies and interaction energies. It was found that the most of the C-H……O intermolecular H-bonds interactions in five stable conformers have some covalent character in nature. The elongation and red shift in IR spectrum of C-H bonds which involve in H-bonds is proved by electron transfers from the lone pairs of the carbonyl O atom of [LAC] to the C-H antibonding orbital of the [Emim]＋. The interaction modes are more favorable when the carbonyl O atoms of [LAC]- interact with the C2-H of the imidazolium ring and the C-H of the ethyl group through the formation of triple H-bonds.