Spectroscopic and structural elucidation of 4-dimethylaminopyridine and its hydrogensquarate

A distortion of the aromatic character and stabilization of the imino-form as a result of the protonation of 4-dimethylaminopyridine was established by IR-, UV- and 1H NMR-spectral analysis of 4-diaminopyridinium hydrogensquarate. Quantum chemical calculations were carried out at MP2 and B3LYP level...

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Veröffentlicht in:Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2008-11, Vol.71 (2), p.695-702
Hauptverfasser: Koleva, Bojidarka B., Kolev, Tsonko, Seidel, Rüdiger W., Tsanev, Tsanko, Mayer-Figge, Heike, Spiteller, Michael, Sheldrick, William S.
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Sprache:eng
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Zusammenfassung:A distortion of the aromatic character and stabilization of the imino-form as a result of the protonation of 4-dimethylaminopyridine was established by IR-, UV- and 1H NMR-spectral analysis of 4-diaminopyridinium hydrogensquarate. Quantum chemical calculations were carried out at MP2 and B3LYP levels of theory and a 6-311++G** basis set with a view to determining the changes in geometrical parameters and IR-spectroscopic characteristics resulting from N py protonation. Linear-dichroic IR-spectroscopy coupled with the orientation techniques of solid samples as liquid crystal suspensions and melted solid polycrystalline films was applied for the identification of the IR-bands, characteristic for the structural fragments of the neutral and imino-form of the pyridine derivative. The spectral results were compared with the structure, obtained by a single crystal X-ray analysis. The salt contains dimmers of hydrogensquarate anions and N py protonated cations of which the former are stabilized by strong intermolecular OH…O interactions (2.552 Å and 143.1(2)°). The 4-diaminopyridinium cation interacts with the anion through moderate NH…O bonds (2.729 Å and 165.0(0)°). Individual cations are π–π stacked with their neighbors at a distance of 3.406 Å.
ISSN:1386-1425
DOI:10.1016/j.saa.2008.01.033