Abstract
Formation constants for complexes of dibenzo-21-crown-7, dibenzo-24-crown-8 and dibenzo-27-crown-9 with the Na+, Cs+ and Tl+ ions have been determined by multinuclear NMR measurements in several nonaqueous solvents. The measurements of the cesium complexes were carried out at different temperatures and the enthalpy and entropy of complexation were determined from the temperature dependence of the formation constants.
The stabilities of these complexes in solvents of low to medium donicity, —nitromethane, acetonitrile, acetone, methanol, and propylene carbonate, vary in the order Tl+>Cs+>Na+. Depending on the relative sizes of the cation and of the ligand cavity, either a three-dimensional ‘wrap-around’ complex or a two-dimensional ‘crown complex’ are formed. For the cesium complexes, the values of ΔH oc and ΔS oc are definitely solvent-dependent and in all cases the complexes are enthalpy stabilized but entropy destabilized. A compensating effect is observed in the variation of the enthalpy and entropy of complexation so that the overall influence of the above solvents on the stability of the complexes is rather limited.
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Shamsipur, M., Rounaghi, G. & Popov, A.I. Sodium-23, cesium-133 and thallium-205 NMR study of sodium, cesium and thallium complexes with large crown ethers in nonaqueous solutions. J Solution Chem 9, 701–714 (1980). https://doi.org/10.1007/BF00645898
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DOI: https://doi.org/10.1007/BF00645898