Structure of 1H-2-oxo-2,3-dihydroimidazo[1,2-a]pyridinium perchlorate studied by X-ray diffraction, DFT calculations and by FTIR and NMR spectroscopy

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• 作者：I. Kowalczyk ; E. Bartoszak-Adamska ; M. Jask&#xf3 ; lski ; Z. Dega-Szafran ; M. Szafran
• 关键词：1H-2-oxo-2 ; 3-dihydroimidazo[1 ; 2-a]pyridinium chloride ; bromide and perchlorate ; X-ray diffraction ; FTIR ; Raman and NMR spectra ; B3LYP calculations ; Hydrogen bonds ; Electrostatic interactions
• 刊名：Journal of Molecular Structure
• 出版年：2010
• 出版时间：15 July 2010
• 年：2010
• 卷：976
• 期：1-3
• 页码：119-128
• 全文大小：789 K

文摘

2-Aminopyridine betaine (1-carboxymethyl-2-aminopyridinium inner salt) forms crystalline complexes with HCl, HBr and HClO₄. These complexes on heating in ethanol cyclize to 1H-2-oxo-2,3-dihydroimidazo[1,2-a]pyridinium chloride (1Ax), bromide (2Ax) and perchlorate (3Ax), respectively. Infrared spectra of the 1H-2-oxo-2,3-dihydroimidazo[1,2-a]pyridinium complexes indicate that the length of the N(1)–H···X⁻ hydrogen bond depends on the counter-ions and increases in the order: Cl⁻ < Br⁻ < ClO₄⁻. In the crystal structure of 3Ax determined by X-ray diffraction, the ClO₄⁻ anion is disordered and the N(1)–H···OClO₃⁻ distance cannot be determined accurately. Three types of cyclic molecules were optimized by the B3LYP/6-31G(d,p) level of theory: type A with N(1)–HX⁻, type B with N(1)H–X hydrogen bonds and type C with electrostatic interactions between the positively charged nitrogen atom N⁺(4) and the counter anion (X⁻ = Cl⁻, Br⁻ or ClO₄⁻). Correlations between the experimental ¹H and ¹³C NMR chemical shifts (δ_exp) and the GIAO/B3LYP/6-31G(d,p) calculated magnetic isotropic shielding tensors (σ_calc) for 3Ao and 3Co, δ_exp = a + bσ_calc, are reported. Tentative assignments of the experimental anharmonic solid state vibrational frequencies of the perchlorate complex, 3Ax, based on the B3LYP/6-31G(d,p) calculated harmonic frequencies, are presented.