Yasaka Yoshiro, Wakai Chihiro, Matubayasi Nobuyuki, Nakahara Masaru
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
J Chem Phys. 2007 Sep 14;127(10):104506. doi: 10.1063/1.2768039.
The rotational correlation time (tau(2R)) is determined for D(2)O (polar) and C(6)D(6) (apolar) in 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) and hexafluorophosphate ([bmim][PF(6)]) by measuring (2)H (D) nuclear magnetic resonance spin-lattice relaxation time (T(1)) in the temperature range from -20 to 110 degrees C. The tau(2R) ratio of water to benzene (tau(WB)) was used as a measure of solute-solvent attraction. tau(WB) is 0.73 and 0.52 in [bmim][Cl] and [bmim][PF(6)], respectively, whereas the molecular volume ratio is as small as 0.11. The slowdown of the water dynamics compared to the benzene dynamics in ionic liquids is interpreted by the Coulombic attractive interaction between the polar water molecule and the anion. As for the anion effect, the rotational dynamics of water solvated by Cl(-) is slower than that solvated by PF(6) (-), whereas the rotational dynamics of benzene is similar in the two ionic liquids. This is interpreted as an indication of the stronger solvation by the anion with a larger surface charge density. The slowdown of the water dynamics via Coulombic solvation is actually significant only at water concentrations lower than approximately 9 mol dm(-3) at room temperature, and it is indistinguishable at temperatures above approximately 100 degrees C. The quadrupolar coupling constants determined for D(2)O and C(6)D(6) in the ionic liquids were smaller by a factor of 2-3 than those in the pure liquid state.
通过测量在-20至110摄氏度温度范围内的2H（D）核磁共振自旋晶格弛豫时间（T1），确定了1-丁基-3-甲基咪唑鎓氯化物（[bmim][Cl]）和六氟磷酸盐（[bmim][PF6]）中D2O（极性）和C6D6（非极性）的旋转相关时间（tau(2R)）。水与苯的tau(2R)比值（tau(WB)）被用作溶质-溶剂吸引力大小的量度。在[bmim][Cl]和[bmim][PF6]中，tau(WB)分别为0.73和0.52，而分子体积比小至0.11。离子液体中与苯动力学相比水动力学的减慢是由极性水分子与阴离子之间的库仑吸引相互作用来解释的。至于阴离子效应，被Cl(-)溶剂化的水的旋转动力学比被PF6(-)溶剂化的水的旋转动力学慢，而苯的旋转动力学在两种离子液体中相似。这被解释为表面电荷密度较大的阴离子具有更强溶剂化作用的一个迹象。通过库仑溶剂化导致的水动力学减慢实际上仅在室温下水浓度低于约9 mol dm(-3)时才显著，并且在高于约100摄氏度的温度下无法区分。在离子液体中为D2O和C6D6测定的四极耦合常数比纯液态时小2至3倍。
