Complexation of the cesium cation by macrocyclic polyethers in various solvents. A cesium-133 nuclear magnetic resonance study of the thermodynamics and kinetics of exchange
Complexation of the cesium cation by macrocyclic polyethers in various solvents. A cesium-133 nuclear magnetic resonance study of the thermodynamics and kinetics of exchange
复制标题
铯阳离子与大环聚醚在各种溶剂中的络合。
DOI：
10.1021/j100532a015
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发表时间：
1977
期刊：
影响因子：
--
通讯作者：
J. L. Dye
中科院分区：
文献类型：
--
作者：
E. Mei;A. I. Popov;J. L. Dye
The formation constants for the complexation of Cs/sup +/ in six solvents by three crown ethers, 18-crown-6, dibenzo-18-crown-6, and dicyclohexyl-18-crown-6, were studied at 25/sup 0/C by cesium-133 NMR techniques. The solvents used, in the approximate order of decreasing first complexation constant for all crown ethers, were pyridine, acetone, propylene carbonate, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide. In all solvents, 18-crown-6 formed both 1:1 and 2:1 (ligand to metal) complexes with enough difference between the complexation constants that the second constant could be determined. The formation of 2:1 complexes by the other two crown ethers was also indicated in most solvents but the second complexation constant could only be measured for the dibenzo-18-crown-6 complex in pyridine. In many cases the first complexation constant was too large to measure by the NMR technique so that only lower bounds could be established. The rate of loss of the Cs/sup +/ ion from dicyclohexyl-18-crown-6 and from monobenzo-2,2,2-cryptand in propylene carbonate was measured as a function of temperature. The activation energy for the latter case (15 kcal mol/sup -1/) is substantially larger than for the crown ether complex (8.5 kcal mol/sup -1/). Although the chemical shifts of both Cs/sup +/ and its 1:1 complex with 18-crown-6more » are strongly solvent dependent, the chemical shift of the 2:1 complex is independent of solvent, indicating that in the ''sandwich'' complex the cesium ion is effectively shielded from the solvent.« less
