先前已有人提出由 BMI-PF6 上的丁基及 PF6
- 之間鍵結空間的
熵改變來說明 Hyper Anion Preference (HAP) 的變化。為了證實此論
點，我們將 BMI+
的丁基置換成羥乙基而得到1-羥乙基-3-甲基咪唑六
氟磷酸鹽(HEMIM-PF6)，再與共溶劑混合，並利用 NMR 技術於變溫
度(300K-320K)及變濃度(X=0.1-0.5)的條件下測量其擴散係數、遲緩
時間及二維光譜(1H-NOESY, 1H,19F-HOESY)。
首先，我們可從 BMI-PF6 及 HEMIM-PF6 兩種混合系統的 1H,
19F-HOESY 光譜之差異說明 HAP 值的下降與熵的改變有關。BMIPF6/
TFE 混合系統中，TFE 最後會與丁基形成氫鍵而佔據 PF6
- 原本
鍵結的空間，然而於 HEMIM-PF6 系統卻看不到該現象，此結果顯
示 HEMIM-PF6 系統有較多的 PF6
- 與陽離子形成鍵結而降低其運
動能力。換句話說，即由丁基轉換成羥乙基而造成 PF6
- 亂度下降。
HEMIM-PF6 系統中，PF6
- 的運動能力降低亦可經由測得 BMI
-PF6 與 HEMIM-PF6 彼此間的擴散係數及遲緩時間之比較而進一步
得到證實。

We have previously proposed the entropy view of the butyl group allowing
ample space for the flow of PF6 anion to account for the large values of Hyper Anion
Preference (HAP) observed for the BMIPF6 ionic liquid system. In order to verify
this entropy argument, the butyl group of BMI cation has been replaced by the
hydroxyethyl group (CH2CH2- OH). The NMR diffusion measurements, 1H-NOESY,
1H,19F-HOESY and spin-lattice relaxation experiments have been extended to the
1-(2-hy -droxyethyl)-3-methylimidazolium hexafluorophosphate (HEMIMPF6) ionic
liquid system.
The HAP values were dropped due to the above-state replacement, which
provides the first supporting evidence of the “Entropy Argument”. This is further
supported by the difference of the 1H,19F-HOESY spectra recorded for BMIPF6 and
HEMIMPF6. The occupation of TFE on butyl in the BMIPF6/TFE mixture will
finally repel the connection of PF6 anion and the butyl through space. For the
HEMIMPF6 analogues, the occupation of TFE on hydroxyethyl group, however,
disappear through analysis of the HOESY spectra. These results are consistent with
the more localized (or less mobile) PF6 anion motion in the HEMIMPF6 ionic liquid
system. In other words, the entropy of PF6 anion decreases as the butyl group is
substituted by the CH2CH2OH.
The localization of PF6 anion has been further verified by the shorter T1 found
for PF6 anion in HEMIMPF6 ionic liquid system compared in the BMIPF6 system
since a more hindered reorientation. The magn- itudes of translation diffusion
measured by PGSE-NMR experiments, again, reveal that PF6 anion is more hindered
in HEMIMPF6 ionic liquid system. Furthermore the changes of chemical shift data
are understood based on the hindered dynamic behaviors of PF6 anion.

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