Interplay of Lewis acidity, intramolecular O→Sn interactions and selectivity: organotin-functionalized crown ethers as ditopic hosts for sodium and potassium halides.

The increased Lewis acidity in organotin-functionalized crown ethers XSnCH[19]-crown-6 (5, X = I; 6, X = Br; 7, X = Cl) not only resulted in ditopic complexation of sodium/potassium halides, but also offers an excellent strategy to manipulate through intramolecular O→Sn interactions the selectivity of the crown ether moiety towards Na/K depending on the solvent.