Understanding the impact of the central atom on the ionic liquid behavior: Phosphonium vs ammonium cations
Understanding the impact of the central atom on the ionic liquid behavior: Phosphonium vs ammonium cations
复制标题
DOI：
10.1063/1.4864182
复制
发表时间：
2014-02-14
影响因子：
4.4
通讯作者：
Coutinho, Joao A. P.
中科院分区：
文献类型：
--
作者：
Carvalho, Pedro J.;Ventura, Sonia P. M.;Coutinho, Joao A. P.
通过测量密度、粘度、熔融温度、无限稀释活度系数、折射率和对费氏弧菌的毒性，研究了阳离子中心原子对铵基和磷基离子液体对行为的影响。所有被研究的性质都受到阳离子中心原子性质的影响，以氨为基础的离子液体呈现出更高的密度、粘度、熔化温度和焓。无限稀释活度系数表明，氨基离子液体对非极性溶剂的无限稀释活度系数略高，对极性溶剂的无限稀释活度系数略低，表明氨基离子液体的极性略高。这些化合物的毒性较同系磷低，这是完全一致的。为了解释这种行为，在BP-TZVP理论水平上对孤立离子对进行了量子化学气相DFT计算。利用电子密度结果推导出确定的最小构象的静电势。静电电位衍生的CHelpG和自然居群分析电荷显示，四烷基膦基离子液体阳离子的P原子比四烷基铵基类似IL阳离子中的N原子带更多正电荷，并且与各自的同类磷酸盐相比，四烷基铵离子液体阳离子中出现了明显的电荷离域。认为这种电荷离域是引起铵基离子液体极性增强的原因，解释了所观察到的热物理性质的变化。(C) 2014 AIP出版有限责任公司
The influence of the cation's central atom in the behavior of pairs of ammonium- and phosphonium-based ionic liquids was investigated through the measurement of densities, viscosities, melting temperatures, activity coefficients at infinite dilution, refractive indices, and toxicity against Vibrio fischeri. All the properties investigated are affected by the cation's central atom nature, with ammonium-based ionic liquids presenting higher densities, viscosities, melting temperatures, and enthalpies. Activity coefficients at infinite dilution show the ammonium-based ionic liquids to present slightly higher infinite dilution activity coefficients for non-polar solvents, becoming slightly lower for polar solvents, suggesting that the ammonium-based ionic liquids present somewhat higher polarities. In good agreement these compounds present lower toxicities than the phosphonium congeners. To explain this behavior quantum chemical gas phase DFT calculations were performed on isolated ion pairs at the BP-TZVP level of theory. Electronic density results were used to derive electrostatic potentials of the identified minimum conformers. Electrostatic potential-derived CHelpG and Natural Population Analysis charges show the P atom of the tetraalkylphosphonium-based ionic liquids cation to be more positively charged than the N atom in the tetraalkylammonium-based analogous IL cation, and a noticeable charge delocalization occurring in the tetraalkylammonium cation, when compared with the respective phosphonium congener. It is argued that this charge delocalization is responsible for the enhanced polarity observed on the ammonium based ionic liquids explaining the changes in the thermophysical properties observed. (C) 2014 AIP Publishing LLC.