title: Mechanochemical preparation of hydrogen-bonded adducts between the diamine 1,4-diazabicyclo[2.2.2]octane and dicarboxylic acids of variable chain length: an X-ray diffraction and solid-state NMR study.
abstract: Mechanical mixing of solid dicarboxylic acids of variable chain length HOOC(CH(2))(n)COOH (n = 1-7) with solid 1,4-diazabicyclo[2.2.2]octane generates the corresponding salts or co-crystals of the formula [N(CH(2)CH(2))(3)N]-H-[OOC(CH(2))(n)COOH] (n=1-7). Preparation of the same systems from solution has been instrumental for a full characterization of the mechanochemical products by means of single-crystal and powder-diffraction X-ray analyses, as well as by solid-state NMR. The acid-base adducts, whether involving proton transfer from the COOH group to the N-acceptor, that is having ((-))O...H-N((+)) interactions, or the formation of neutral O-H...N hydrogen bonds, show a melting point alternation phenomenon analogous to that shown by the neutral carboxylic acids. The carbon chemical shift tensors of the COOH group obtained from the sideband intensity of low speed spinning NMR spectra provide a reliable criterion for assigning the protonation state of the adducts.
authors.affiliation: Dipartimento di Chimica G. Ciamician, Università di Bologna, Via F. Selmi 2, 40126 Bologna, Italy. dbraga@ciam.unibo.it
authors.forename: Dario
authors.initials: D
authors.lastname: Braga
authors.forename: Lucia
authors.initials: L
authors.lastname: Maini
authors.forename: Giorgiana
authors.initials: G
authors.lastname: de Sanctis
authors.forename: Katia
authors.initials: K
authors.lastname: Rubini
authors.forename: Fabrizia
authors.initials: F
authors.lastname: Grepioni
authors.forename: Michele R
authors.initials: MR
authors.lastname: Chierotti
authors.forename: Roberto
authors.initials: R
authors.lastname: Gobetto