Structure of 2,3-dicarboxy-1-methylpyridinium chloride studied by X-ray diffraction, DFT calculation, NMR, FTIR and Raman spectra

The structure of 2,3-dicarboxy-1-methylpyridinium chloride (1) has been studied by X-ray diffraction, DFT calculations, NMR, FTIR and Raman spectra. The crystals are monoclinic, space group P21/c. Chloride anion links two 2,3-dicarboxy-1-methylpyridinium cations into infinite zigzag chains down the [0 0 1] direction by the OH⋯Cl−⋯HO hydrogen bonds of 2.970(2) and 3.011(2) Å. Hydrogen bond lengths in single molecules (2–4) optimized by the B3LYP/6-311++G(d,p) approach depend on the environment and intramolecular O·H·O hydrogen bond. Linear correlations between the experimental 13C and 1H chemical shifts (δexp) of the investigated compound in DMSO-d6 and the GIAO/B3LYP/6-311++G(d.p) magnetic isotropic shielding constants (σcalc) calculated using the screening solvation model (COSMO), δexp = a + b σcalc, are reported. The FTIR spectrum of the solid compound is consistent with the X-ray structure. The deformation in-plane and out-of-plane OH vibrations, both in FTIR and second-derivative (d2) spectra, appear as two bands consistent with the OH⋯Cl−⋯HO arrangement.