1-乙基-3-甲基咪唑和PF-6离子液体的理论研究

采用Hartree-Fock和密度泛函理论方法研究1-乙基-3-甲基咪唑阳离子(EMIM )、PF6-、EMIM -PF6-离子对。氢原子、碳原子、氮原子、氟原子和磷原子在6-31 (d,p)基组水平上,采用Gaussian94软件包给EMIM 、PF6-及12个EMIM -PF6-离子的初始结构做全优化和频率分析。比较研究所优化结构和能量的性质。计算结果表明最低能量结构的EMIM -PF6-阴阳离子对相互作用能,在Hartree-Fock水平上为326.6 kJ／mol、在密度泛函理论上为328.8 kJ／mol。阳离子不对称、阴阳离子间距较大、阴阳离子电荷的分散使①静电作用降低,导致离子液体熔点较低。②EMIM 氢原子的正电荷增加、PF6-氟原子的负电荷增加,导致C-H---F氢键相互作用增强。从而在离子液体中起重要作用。本文着重考察了EMIM 和PF6-相互作用的三种氢键方式。

Theoretical study on room temperature ionic liquid based 1-ethyl-3-methyl-imidazolium and PF-6

The Hartree-Fock method and density functional theory have been employed to investigate electronic structures of EMIM (1-ethyl-3-methylimidazolium ) , PF6- , EMIM -PF6- pairs. Full optimization and frequency analyses of EMIM , PF6- and twelve initial EMIM -PF6- geometries have been carried out using Gaussian-94 soft-package at 6-31 G( d,p) basis set level for hydrogen, carbon, nitrogen, fluorine and phosphorus atoms. The electronic structures of lowest energy of EMIM -PF6-, single EMIM , PF6- have been comparatively studied. The calculated results showed that interaction energy between EMIM and PF6- is 326. 6 kJ/mol at Hartree-Fock level and 328. 8 kJ/mol at B3LYP level. The bulky asymmetry of EMIM , the long distance between cation and anion, the charge dispersion result in decrease of electrostatic interaction between EMIM and PF6- , this make ionic liquid melting point low. The C-H---F interaction reinforced by charge dispersion increases, this means that positive charge of hydrogen atom for EMIM and negative charge of fluorine atom for PF6- increase. The charge assistance makes hydrogen bond play an important role in the cohesion of ionic liquid. The three hydrogen bonding models of single one hydrogen bond formation, multi hydrogen bonds formation and proton transfer between C2 of EMIM and one F of PF6- were principally depicted.