CROWN ETHERS WITH A LEWIS ACIDIC CENTER - A NEW CLASS OF HETEROTOPIC HOST MOLECULES

The incorporation of a Lewis acid center in a crown ether as in 1 leads to a host molecule, which may either complex a cation leaving the counter ion ''outside'' (monotopicity) or bind both cation and anion simultaneously, the latter with ate complexation (di- or heterotopicity). Host 1 displays a selectivity never seen before in the complexation of series of potassium salts KX (X = F, Cl, Br, I, SCN, CN, OCH3).