The Hartree-Fock and DFT/B3LYP methods have been employed to investigate the electronic structures of 1-ethyl-3-methyl-imidazolium cation （EMIM＋）, BF4^-, PF6^-, EMIM＋BF4^-, and EMIM＋-PF6^- using the Gaussian-94 s...The Hartree-Fock and DFT/B3LYP methods have been employed to investigate the electronic structures of 1-ethyl-3-methyl-imidazolium cation （EMIM＋）, BF4^-, PF6^-, EMIM＋BF4^-, and EMIM＋-PF6^- using the Gaussian-94 soft-package at 6-31＋G（d,p） basis set level for hydrogen, carbon, nitrogen, boron, phosphorus, and fluorine atoms. Comparison of the electronic structures of the lowest energy of EMIM＋- BF4^- and EMIM＋-PF6^- pairs, and single EMIM＋, BF4^- and PF6^- showed that the optimized EMIM＋-BF4^- and EMIM＋-PF6^- pair conformers were BF4^- and PF6^- outside the 5-ring plane between the ethyl group and the methyl group. The cohesion of C H. … F hydrogen bond between cation and anion is reinforced by charge assistance. The interaction energy between EMIM＋ and PF6 is 328.8 kJ/mol at the B3LYP level and 326.6 kJ/mol at the Hartree-Fock level, whereas that between EMIM＋ and BF4 is 353.5 kJ/mol at the B3LYP level and 350.5 kJ/mol at the Hartree-Fock level. The low energy interactions caused by bulky asymmetric EMIM＋, and charge dispersion of cation and anion give rise to the low melting point of ionic liquid EMIM＋-BF4^- and EMIM＋-PF6^-. The two hydrogen bonding models of single hydrogen bond formation, and the hydrogen transfer between C2 in EMIM＋ and F in BF4^- or PF6^- were principally depicted.展开更多
文摘The Hartree-Fock and DFT/B3LYP methods have been employed to investigate the electronic structures of 1-ethyl-3-methyl-imidazolium cation （EMIM＋）, BF4^-, PF6^-, EMIM＋BF4^-, and EMIM＋-PF6^- using the Gaussian-94 soft-package at 6-31＋G（d,p） basis set level for hydrogen, carbon, nitrogen, boron, phosphorus, and fluorine atoms. Comparison of the electronic structures of the lowest energy of EMIM＋- BF4^- and EMIM＋-PF6^- pairs, and single EMIM＋, BF4^- and PF6^- showed that the optimized EMIM＋-BF4^- and EMIM＋-PF6^- pair conformers were BF4^- and PF6^- outside the 5-ring plane between the ethyl group and the methyl group. The cohesion of C H. … F hydrogen bond between cation and anion is reinforced by charge assistance. The interaction energy between EMIM＋ and PF6 is 328.8 kJ/mol at the B3LYP level and 326.6 kJ/mol at the Hartree-Fock level, whereas that between EMIM＋ and BF4 is 353.5 kJ/mol at the B3LYP level and 350.5 kJ/mol at the Hartree-Fock level. The low energy interactions caused by bulky asymmetric EMIM＋, and charge dispersion of cation and anion give rise to the low melting point of ionic liquid EMIM＋-BF4^- and EMIM＋-PF6^-. The two hydrogen bonding models of single hydrogen bond formation, and the hydrogen transfer between C2 in EMIM＋ and F in BF4^- or PF6^- were principally depicted.
