Yoshida Yukihiro, Kondo Masatoshi, Saito Gunzi
Research Institute, Meijo University, Shiogamaguchi 1-501 Tempaku, Nagoya 468-8502, Japan.
J Phys Chem B. 2009 Jul 2;113(26):8960-6. doi: 10.1021/jp903242w.
A series of ionic liquids based on five kinds of polycyano 1,1,3,3-tetracyanoallyl anions with 2-substituents having different electron-withdrawing or -donating abilities were prepared. The influence of the chemical modification on their thermal properties, viscosity, ionic conductivity, ion association, and solvatochromic shifts was characterized and compared with the case of previously reported polycyano anions, N(CN)(2)(-) and C(CN)(3)(-). Among the 1-butyl-3-methylimidazolium (BMI) salts, cyano-substituted (i.e., 1,1,2,3,3-pentacyanoallyl anion) salt has the highest melting point (42 degrees C), possibly indicating the importance of high local symmetry over decreased interionic CN...cation interactions due to the limited electron densities on terminal nitrogens of the anions, predicted by ab initio calculations. In the liquid state, methoxy-substituted (i.e., 2-methoxy-1,1,3,3-tetracyanoallyl anion) salt has the highest fluidity and ionic conductivity, associated with the significant conformational degree of freedom in the methoxy group. Although the ion diffusivity has no definite correlation with the Hammett parameter of the substituents, the introduction of electron-withdrawing cyano or cyanomethyl (i.e., 2-cyanomethyl-1,1,3,3-tetracyanoallyl anion) groups leads to the decrease in the degree of ion association and solvent donor ability, which were manifested in the Walden rule deviation and solvatochromic shift, respectively.
制备了一系列基于五种带有不同吸电子或供电子能力的2-取代基的多氰基1,1,3,3-四氰基烯丙基阴离子的离子液体。表征了化学修饰对其热性能、粘度、离子电导率、离子缔合和溶剂化显色位移的影响，并与先前报道的多氰基阴离子N(CN)(2)(-)和C(CN)(3)(-)的情况进行了比较。在1-丁基-3-甲基咪唑鎓（BMI）盐中，氰基取代的（即1,1,2,3,3-五氰基烯丙基阴离子）盐具有最高熔点（42℃），这可能表明高局部对称性比由于阴离子末端氮原子上电子密度有限导致的离子间CN...阳离子相互作用减弱更为重要，这是由从头算计算预测的。在液态下，甲氧基取代的（即2-甲氧基-1,1,3,3-四氰基烯丙基阴离子）盐具有最高的流动性和离子电导率，这与甲氧基中显著的构象自由度有关。尽管离子扩散率与取代基的哈米特参数没有明确的相关性，但吸电子氰基或氰甲基（即2-氰甲基-1,1,3,3-四氰基烯丙基阴离子）基团的引入导致离子缔合程度和溶剂给体能力降低，分别表现为瓦尔登规则偏差和溶剂化显色位移。
