Molecular design of crown ethers. Part 8. Substitution and lariat effect upon cation complexation with 1,4,7,10,13-pentaoxacyclohexadecane (16-crown-5) derivatives in solvent extraction and in homogeneous solution

The effects of a donating sidearm introduced into 1,4,7,10,13-pentaoxacyclohexadecane (16-crown-5) upon its binding abilities and relative cation selectivities for alkali-metal ions were examined comparatively in solvent extraction and in the homogeneous phase. In sharp contrast to much enhanced extractabilities and relative cation selectivities observed in the solvent extraction of aqueous alkali-metal picrates with a 16-crown-5 lariat, rather reduced complex stability constants and selectivities were obtained in a conductance study in methanol. This obviously conflicts with the basic concept of the lariat effect and may require further verification of its applicability to other ligand and solvent systems.