期刊
INORGANICA CHIMICA ACTA
卷 357, 期 2, 页码 541-547出版社
ELSEVIER SCIENCE SA
DOI: 10.1016/j.ica.2003.08.011
关键词
complex stability constants; transfer activity coefficients; nitromethane; alkali metal ions; crown ethers; selectivity
Stability constants for the 1:1 complexes of Na+, K+, Rb+, and Cs+ with dibenzo-18-crown-6 (DB18C6) and dibenzo-24-crown-8 (DB24C8) have been determined by conductometry at 25 degreesC in a poorly solvating solvent, nitromethane. For both the crown ethers, the stability constant decreases with increasing metal ion size, Na+ > K+ > Rb+ > Cs+, regardless of the size compatibility between the metal ions and the ligand cavities. A comparison of the results with those in several other solvents (S: acetonitrile, propylene carbonate, water, methanol, and N,N-dimethylformamide) leads to the conclusion that the selectivity sequence of these crown ethers in nitromethane agrees with the intrinsic one in the absence of a solvent. Transfer activity coefficients of the crown ethers and their complexes from nitromethane to S have been determined to evaluate the solute-solvent interactions. It is shown that DB24C8 shields the alkali metal ions more effectively from the solvents than DB18C6 because of the larger number of oxygen atoms and the more flexible structure of DB24C8. Regarding the complexation in nitromethane as a reference, the complex stability and selectivity in S are discussed. The selectivities of these crown ethers in water, methanol, and N, N-dimethylformamide, which apparently obey the size-fit concept, are largely due to the solvation of the free alkali metal ions. (C) 2003 Elsevier B.V. All rights reserved.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据