Ionic liquids based on dicyanamide anion: influence of structural variations in cationic structures on ionic conductivity.
Ionic liquids based on dicyanamide anion: influence of structural variations in cationic structures on ionic conductivity.
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DOI：
10.1021/jp067055t
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发表时间：
2007-01
期刊：
影响因子：
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通讯作者：
Y. Yoshida;Osamu Baba;G. Saito
中科院分区：
文献类型：
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作者：
Y. Yoshida;Osamu Baba;G. Saito
以不同烷基链长的1-烷基-3-甲基咪唑阳离子和不同环结构的含乙基杂环阳离子为原料，合成了一系列双氰胺[N（CN）2]基离子液体，研究了其结构变化对其热性能、密度、电化学窗口、粘度、离子电导率和溶致变色效应的影响。我们发现，1，3-二甲基咪唑鎓盐在不含卤代阴离子的离子液体中显示出最高的离子电导率（在25 ℃下为3.6 × 10（-2）S cm（-1）），并且烷基链的延长导致流动性和离子电导率的显著降低。此外，这种伸长引起液体中离子缔合度的增加，这主要是由烷基链之间的货车范德华相互作用引起的。具有1-乙基-2-甲基吡唑鎓（EMP）和N-乙基-N-甲基吡咯烷鎓（PY（12））阳离子以及1-乙基-3-甲基咪唑鎓（EMI）阳离子的N（CN）2盐在室温（RT）下为液体，而N-乙基噻唑鎓盐在较高温度（57 ℃）下显示熔融事件。在三种含乙基阳离子的室温离子液体中，室温离子电导率的顺序为EMI > PY（12）> EMP，这与室温下流动性的顺序（EMI > EMP > PY（12））不一致。这种差异源于PY（12）盐中的高度离子解离，这表现在瓦尔登规则偏差和溶致变色效应中。还制备了一系列EMI盐的N（CN）2/C（CN）3二元混合物。RT离子电导率随C（CN）3阴离子摩尔分数的增加而线性下降。
A series of dicyanamide [N(CN)2]-based ionic liquids were prepared using 1-alkyl-3-methylimidazolium cations with different alkyl chain lengths and ethyl-containing heterocyclic cations with different ring structures, and the influence of such structural variations on their thermal property, density, electrochemical window, viscosity, ionic conductivity, and solvatochromic effects was investigated. We found that the 1,3-dimethylimidazolium salt shows the highest ionic conductivity among ionic liquids free from halogenated anions (3.6 x 10(-2) S cm(-1) at 25 degrees C), and the elongation of the alkyl chain causes the pronounced depression of fluidity and ionic conductivity. Also, such an elongation gives rise to the increase in the degree of ion association in the liquids, mainly caused by the van der Waals interactions between alkyl chains. N(CN)2 salts with 1-ethyl-2-methylpyrazolium (EMP) and N-ethyl-N-methylpyrrolidinium (PY(12)) cations as well as 1-ethyl-3-methylimidazolium (EMI) cation are liquids at room temperature (RT), while the N-ethylthiazolium salt shows a melting event at higher temperature (57 degrees C). Among the three RT ionic liquids with ethyl-containing cations, RT ionic conductivity follows the order EMI > PY(12) > EMP, which does not coincide with the order of fluidity at RT (EMI > EMP > PY(12)). Such a discrepancy is originated from a high degree of ion dissociation in the PY(12) salt, which was manifested in the Walden rule deviation and solvatochromic effects. A series of N(CN)2/C(CN)3 binary mixtures of the EMI salts were also prepared. RT ionic conductivity decreases linearly with increasing the molar fraction of C(CN)3 anion.