title: New Upper Rim Pyridine-Bridged Calix[4]arenes: Synthesis and Complexation Properties toward Neutral Molecules and Ammonium Ions in Organic Media.
abstract: 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 complexation properties of these systems in solution toward several neutral molecules having acidic C-H bonds. Additionally, selective complexation of methylammonium tosylate in comparison with other ammonium salts has been observed and the strength of this complexation enhanced by electron-donor ability of the p-substituent on the pyridine moiety of the calixarene host. X-ray crystal structures of endo complexes of host 5with 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.
authors.affiliation: Dipartimento di Chimica Organica ed Industriale, Università di Parma, Viale delle Scienze, 43100 Parma, Italy, and Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica and Centro di Studio per la Strutturistica Diffrattometrica del CNR, Università di Parma, Viale delle Scienze, 43100 Parma, Italy.
authors.forename: Arturo
authors.initials: A
authors.lastname: Arduini
authors.forename: William M.
authors.initials: WM
authors.lastname: McGregor
authors.forename: Andrea
authors.initials: A
authors.lastname: Pochini
authors.forename: Andrea
authors.initials: A
authors.lastname: Secchi
authors.forename: Franco
authors.initials: F
authors.lastname: Ugozzoli
authors.forename: Rocco
authors.initials: R
authors.lastname: Ungaro