title: Nature of urea-fluoride interaction: incipient and definitive proton transfer.
abstract: 1,3-bis(4-nitrophenyl)urea (1) interacts through hydrogen bonding with a variety of oxoanions in an MeCN solution to give bright yellow 1:1 complexes, whose stability decreases with the decreasing basicity of the anion (CH3COO- > C6H5COO- > H2PO4- > NO2- > HSO4- > NO3-). The [Bu4N][1.CH3COO] complex salt has been isolated as a crystalline solid and its molecular structure determined, showing the formation of a discrete adduct held together by two N-H...O hydrogen bonds of moderate strength. On the other hand, the F- ion first establishes a hydrogen-bonding interaction with 1 to give the most stable 1:1 complex, and then on addition of a second equivalent, induces urea deprotonation, due to the formation of HF2-. The orange-red deprotonated urea solution uptakes carbon dioxide from air to give the tetrabutylammonium salt of the hydrogencarbonate H-bond complex, [Bu4N][1.HCO3], whose crystal and molecular structures have been determined.
authors.affiliation: Dipartimento di Chimica Generale, Università di Pavia, via Taramelli 12, 27100 Pavia, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Boiocchi
authors.forename: Laura
authors.initials: L
authors.lastname: Del Boca
authors.forename: David Esteban
authors.initials: DE
authors.lastname: Gómez
authors.forename: Luigi
authors.initials: L
authors.lastname: Fabbrizzi
authors.forename: Maurizio
authors.initials: M
authors.lastname: Licchelli
authors.forename: Enrico
authors.initials: E
authors.lastname: Monzani