NEW UPPER RIM PYRIDINE-BRIDGED CALIX[4]ARENES - SYNTHESIS AND COMPLEXATION PROPERTIES TOWARD NEUTRAL MOLECULES AND AMMONIUM-IONS IN ORGANICMEDIA

A new series of calix[4]arenes, diametrically bridged at the upper rim with pyridino systems, has been synthesized. The shape, rigidity, and chemical structure of the bridge influence the host-guest complexatio n properties of these systems in solution toward several neutral molec ules having acidic C-H bonds. Additionally, selective complexation of methylammonium tosylate in comparison with other ammonium salts has be en observed and the strength of this complexation enhanced by electron -donor ability of the p-substituent on the pyridine moiety of the cali xarene host. X-ray crystal structures of endo complexes of host 5 with malononitrile and nitromethane have been resolved, verifying specific C-H bonding with the hard oxygen and nitrogen atoms of the bridge and the soft aromatic ring of the calixarene.