Anion Partitioning and Ion-Pairing Behavior of Anions in the Extraction of Cesium Salts by 4,5' '-Bis(tert-octylbenzo)dibenzo-24-crown-8 in 1,2-Dichloroethane

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• 作者：Tatiana G. Levitskaia ; Leon Maya ; Gary J. Van Berkel ; Bruce A. Moyer
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：January 8, 2007
• 年：2007
• 卷：46
• 期：1
• 页码：261 - 272
• 全文大小：238K
• 年卷期：v.46,no.1(January 8, 2007)
• ISSN：1520-510X

文摘

A systematic study of anion partitioning and ion pairing was performed for an extraction of individual cesium saltsinto 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-saturated1,2-DCE at 25 ges/entities/deg.gif">C were obtained from equilibrium modeling using the SXLSQI program. The standard Gibbs energyof 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 experimentswas 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 pairingin the 1,2-DCE phase was relatively small, by comparison only a tenth of the discrimination exhibited by the anionpartitioning. 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 crownether upon encapsulation of the Cs⁺ ion, whose weak anion recognition likely reflects the preferential inclusion of1,2-DCE molecules in the clefts. Observed anion extraction selectivity in this system, which may be ascribedpredominantly to solvent-induced Hofmeister bias selectivity toward large charge-diffuse anions, was nearly thesame whether cesium salts were extracted as dissociated ions or ion pairs.