title: Spectroscopic and structural elucidation of 4-dimethylaminopyridine and its hydrogensquarate.
abstract: 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 Npy 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 Npy protonated cations of which the former are stabilized by strong intermolecular OH...O interactions (2.552 angstroms and 143.1(2) degrees). The 4-diaminopyridinium cation interacts with the anion through moderate NH...O bonds (2.729 angstroms and 165.0(0) degrees ). Individual cations are pi-pi stacked with their neighbors at a distance of 3.406 angstroms.
authors.affiliation: Lehrstuhl für Analytische Chemie, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany. Bkoleva@chem.uni-sofia.bg
authors.forename: Bojidarka B
authors.initials: BB
authors.lastname: Koleva
authors.forename: Tsonko
authors.initials: T
authors.lastname: Kolev
authors.forename: Rüdiger W
authors.initials: RW
authors.lastname: Seidel
authors.forename: Tsanko
authors.initials: T
authors.lastname: Tsanev
authors.forename: Heike
authors.initials: H
authors.lastname: Mayer-Figge
authors.forename: Michael
authors.initials: M
authors.lastname: Spiteller
authors.forename: William S
authors.initials: WS
authors.lastname: Sheldrick
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives* / Q000737:chemistry; D003460:Crystallization; D003503:Cyclobutanes / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D013053:Spectrophotometry; D014732:Vibration
chemical_list: D003503:Cyclobutanes; D006859:Hydrogen; D015761:4-Aminopyridine; C003885:4-dimethylaminopyridine