title: Spectroscopic and structural investigation of 2,5-dicarboxy-1-methylpyridinium inner salt.
abstract: The structure of 2,5-dicarboxy-1-methylpyridinium inner salt (1), has been studied by X-ray diffraction, B3LYP/6-311G(d,p) calculations, FTIR, Raman and NMR spectroscopy. The molecules are linked by short intermolecular and asymmetric O-H⋯O hydrogen bonds of 2.486(2)Å between carboxyl and carboxylate groups of neighboring molecules into infinite chains. The hydrogen bonds in the molecules optimized by the B3LYP/6-311G(d,p) approach in trimer (2) and dimer (3) are slightly longer than in the crystal. The FTIR spectrum of the investigated inner salt is dominated by a broad and intense absorption in the 1500-800 cm(-1) region attributed to the ν(as)(OHO) and γ(OHO) vibrations of the strong hydrogen bond. In the Raman spectrum the broad absorption is absent. Linear correlations, δ(exp)=a+b σ(calc) between the experimental (1)H and (13)C NMR chemical shifts (δ(exp)) of the investigated inner salt in D2O and the calculated magnetic isotropic shielding constants (σ(calc)) for the optimized monomer (4a) solvated in water are reported. The pKa value for 1 of 2.31±0.02 was determined by the potentiometric titration.
authors.affiliation: Faculty of Chemistry, A. Mickiewicz University, 61-614 Poznań, Poland. Electronic address: pbar@amu.edu.pl.
authors.forename: P
authors.initials: P
authors.lastname: Barczyński
authors.affiliation: Faculty of Chemistry, A. Mickiewicz University, 61-614 Poznań, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Komasa
authors.affiliation: Faculty of Chemistry, A. Mickiewicz University, 61-614 Poznań, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Katrusiak
authors.affiliation: Faculty of Chemistry, A. Mickiewicz University, 61-614 Poznań, Poland.
authors.forename: Z
authors.initials: Z
authors.lastname: Dega-Szafran
authors.affiliation: Faculty of Chemistry, A. Mickiewicz University, 61-614 Poznań, Poland.
authors.forename: Ł
authors.initials: Ł
authors.lastname: Nowaczyk
authors.affiliation: Faculty of Chemistry, A. Mickiewicz University, 61-614 Poznań, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Ratajczak-Sitarz
authors.affiliation: Faculty of Chemistry, A. Mickiewicz University, 61-614 Poznań, Poland.
authors.forename: M
authors.initials: M
authors.lastname: Szafran
mesh_terms: D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D009525:Niacin / Q000031:analogs & derivatives* / Q000737:chemistry; D011726:Pyridinium Compounds / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics
chemical_list: D011726:Pyridinium Compounds; D009525:Niacin; C014677:1-methylpyridinium
keywords: 2,5-Dicarboxy-1-methylpyridinium inner salt; DFT calculations; FTIR and NMR spectra; Hydrogen bonds; X-ray diffraction