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
✍ Scribed by Dario Braga; Lucia Maini; Giorgiana de Sanctis; Katia Rubini; Fabrizia Grepioni; Michele R. Chierotti; Roberto Gobetto
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 266 KB
- Volume
- 9
- Category
- Article
- ISSN
- 0947-6539
No coin nor oath required. For personal study only.
✦ Synopsis
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⋅⋅⋅HN^(+)^ interactions, or the formation of neutral OH⋅⋅⋅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.