Levitskaia Tatiana G, Maya Leon, Van Berkel Gary J, Moyer Bruce A
Chemical Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37830-6119, USA.
Inorg Chem. 2007 Jan 8;46(1):261-72. doi: 10.1021/ic061605k.
A systematic study of anion partitioning and ion pairing was performed for an extraction of individual cesium salts into 1,2-dichloroethane (1,2-DCE) using 4,5' '-bis(tert-octylbenzo)dibenzo-24-crown-8 as the cesium receptor. Equilibrium constants corresponding to the extraction of ion pairs and dissociated ions, formation of the 1:1 cesium/crown complex (confirmed by electrospray mass spectrometry), and dissociation of the ion pairs in water-saturated 1,2-DCE at 25 degrees C were obtained from equilibrium modeling using the SXLSQI program. The standard Gibbs energy of partitioning between water and water-saturated 1,2-DCE was determined for picrate, permanganate, trifluoromethanesulfonate, methanesulfonate, trifluoroacetate, and acetate anions. The dissociation of the organic-phase complex ion pair [Cs(4,4' '-bis(tert-octylbenzo)dibenzo-24-crown-8]+NO3- observed in the extraction experiments was shown to be consistent with the dissociation constant determined independently by conductance measurements. As attributed to the large effective radius of the complex cation, the evident anion discrimination due to ion pairing in the 1,2-DCE phase was relatively small, by comparison only a tenth of the discrimination exhibited by the anion partitioning. Only chloride and picrate exhibit evidence for significantly greater-than-expected ion-pairing tendency. These results provide insight into the inclusion properties of the clefts formed by opposing arene rings of the crown ether upon encapsulation of the Cs+ ion, whose weak anion recognition likely reflects the preferential inclusion of 1,2-DCE molecules in the clefts. Observed anion extraction selectivity in this system, which may be ascribed predominantly to solvent-induced Hofmeister bias selectivity toward large charge-diffuse anions, was nearly the same whether cesium salts were extracted as dissociated ions or ion pairs.
使用4,5''-双（叔辛基苯并）二苯并-24-冠-8作为铯受体，对将个别铯盐萃取到1,2-二氯乙烷（1,2-DCE）中的阴离子分配和离子对进行了系统研究。通过使用SXLSQI程序进行平衡建模，获得了与离子对和离解离子的萃取、1:1铯/冠醚配合物的形成（通过电喷雾质谱法确认）以及在25℃水饱和的1,2-DCE中离子对的解离相对应的平衡常数。测定了苦味酸盐、高锰酸盐、三氟甲磺酸盐、甲磺酸盐、三氟乙酸盐和乙酸根阴离子在水和水饱和的1,2-DCE之间分配的标准吉布斯自由能。萃取实验中观察到的有机相复合离子对[Cs(4,4''-双（叔辛基苯并）二苯并-24-冠-8]+NO3-的解离与通过电导测量独立测定得解离常数一致。由于复合阳离子的有效半径较大，1,2-DCE相中离子对引起的明显阴离子歧视相对较小，相比之下仅为阴离子分配所表现出歧视的十分之一。只有氯离子和苦味酸盐表现出明显大于预期的离子对形成倾向。这些结果深入了解了冠醚相对的芳环在包封Cs+离子时形成的裂缝的包合性质，其弱阴离子识别可能反映了1,2-DCE分子在裂缝中的优先包合。该体系中观察到的阴离子萃取选择性，主要归因于溶剂诱导的对大电荷分散阴离子的霍夫迈斯特偏好选择性，无论铯盐是以离解离子还是离子对形式被萃取，其选择性几乎相同。
