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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
Author(s) -
Braga Dario,
Maini Lucia,
de Sanctis Giorgiana,
Rubini Katia,
Grepioni Fabrizia,
Chierotti Michele R.,
Gobetto Roberto
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200304940
Subject(s) - chemistry , crystallography , protonation , hydrogen bond , intramolecular force , adduct , octane , x ray crystallography , solid state nuclear magnetic resonance , nmr spectra database , diffraction , stereochemistry , molecule , spectral line , organic chemistry , nuclear magnetic resonance , astronomy , ion , physics , optics
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.