Structure of 3,4-dicarboxy-1-methylpyridinium chloride studied by X-ray diffraction, DFT calculations, NMR and FTIR spectra

The structure of 3,4-dicarboxy-1-methylpyridinium chloride (34DCMPCl) has been studied by X-ray diffraction, DFT calculations, NMR and FTIR spectra. The crystals are monoclinic, space group P21. Chloride anion links two 3,4-dicarboxy-1-methylpyridinium cations into infinite zigzag chains down [0 1 0] by the OH⋯Cl−⋯HO hydrogen bonds of 2.953(2) and 2.968(2) Å. Hydrogen bonds in single molecules optimised by the B3LYP/6-31G(d,p) approach depend on the environment. In vacuum (2 and 3) the hydrogen bonded proton is linked with chloride atom (Cl–H⋯O), while in DMSO (4) the structure is similar to that in the crystal (Cl⋯H–O). Linear correlations between the experimental 13C and 1H chemical shifts (δexp) of the investigated compound in DMSO-d6 and the calculated GIAO/B3LYP/6-31G(d,p) magnetic isotropic shielding tensors (σcalc) using the screening solvation model (COSMO), δexp = a + bσcalc, are reported. The FTIR spectrum of the solid compound is consistent with the X-ray structure. The deformation absorptions in plane and out of plane, both in FTIR and second-derivative spectra (d2), appear as two bands and confirm the OH⋯Cl−⋯HO hydrogen bonds formation.