确定1-烷基-3-甲基咪唑六氟磷酸盐系列中缺失的晶体结构：对结构-性能关系的影响,Crystal Growth & Design

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确定1-烷基-3-甲基咪唑六氟磷酸盐系列中缺失的晶体结构：对结构-性能关系的影响
Crystal Growth & Design ( IF 3.2 ) Pub Date : 2013-10-31 00:00:00 , DOI: 10.1021/cg401293g
Takatsugu Endo ₁ , Hyuma Masu ₂ , Kozo Fujii ₃ , Takeshi Morita ₃ , Hiroko Seki ₂ , Sabyasachi Sen ₁ , Keiko Nishikawa ₃

Affiliation

我们对两种1-烷基-3-甲基咪唑六氟磷酸盐（[C _n mim] PF ₆），[C ₁ mim] PF ₆和[C ₃ mim] PF ₆进行了单晶X射线衍射分析。前者的热力学亚稳态结晶相（β相）是通过从毛细管中的熔体中结晶而获得的，用于结晶学分析。[C ₁ mim] PF ₆的β相中的阳离子和阴离子表现出比稳定α相更高的点群对称性。该结果表明与β多晶型物（314K）的熔点显着低于α多晶型物（364K）的熔点这一事实是一致的。[C ₃ mim] PF ₆的晶体结构似乎是咪唑基室温离子液体的晶体特征的典型特征。阳离子构象介于[C ₂ mim] PF ₆和[C ₄ mim] PF ₆的晶体结构的那些特征之间。一起考虑时，[C _n mim] PF ₆系列的所有晶体学数据（n= 1-4）证明了这些盐中烷基链长依赖性对结构堆积的影响。仅基于公式单位体积，即可计算出这些结构的自由体积分数，并将其与晶格能量进行比较。结果表明，咪唑鎓阳离子的烷基链长的差异不会随晶体结构的晶格能单调变化，后者也取决于结构中各组成离子的堆积效率。

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Determination of Missing Crystal Structures in the 1-Alkyl-3-methylimidazolium Hexafluorophosphate Series: Implications on Structure–Property Relationships

We have performed single crystal X-ray diffraction analyses of two 1-alkyl-3-methylimidazolium hexafluorophosphate ([C_nmim]PF₆) salts, [C₁mim]PF₆, and [C₃mim]PF₆. The thermodynamically metastable crystalline phase (β phase) of the former was obtained by crystallization from the melt in a capillary for the crystallographic analysis. Both the cation and the anion in the β phase of [C₁mim]PF₆ show higher point group symmetry than those in the stable α phase. This result is shown to be consistent with the fact that the melting point of the β polymorph (314 K) is significantly lower than that of the α polymorph (364 K). The crystal structure of [C₃mim]PF₆ seems to be typical of that characteristic of the crystals of imidazolium-based room temperature ionic liquids. The cation conformation is the one in between those characteristic of the crystal structures of [C₂mim]PF₆ and [C₄mim]PF₆. When taken together, all crystallographic data for the [C_nmim]PF₆ series (n = 1–4) demonstrate the influence of the alkyl chain length dependence on structural packing in these salts. The free volume fractions for these structures are calculated and compared to the lattice energy simply based on formula unit volume. It is shown that the difference in the alkyl chain length of the imidazolium cations does not monotonically change with the lattice energy of the crystal structure, and the latter also depends on the packing efficiency of the constituent ions in the structure.

更新日期：2013-10-31

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