Structure of 1-carboxymethylpyridinium-4-carboxylate inner salt studied by X-ray diffraction, DFT calculations, vibrational and NMR spectra

The structure of 1-carboxymethylpyridinium-4-carboxylate inner salt has been studied by X-ray diffraction, B3LYP calculations, FTIR, Raman and NMR spectroscopic techniques. The crystals are monoclinic, space group P21/n. Each molecule is engaged in two short asymmetric O·H·O hydrogen bonds (2.449(2) and 2.481(2) Å) with two adjacent molecules through head-to-head and tail-to-tail connections. Structures of 10 linear and two cyclic most stable complexes have been optimized by the B3LYP level of theory and the results have been compared with the X-ray data. Energy stabilizations, ΔE = Ecomplex − Ecomponents, caused by H-bond and electrostatic interactions between the opposite charged atoms (N+ and O−) have been determined and analyzed. The FTIR spectrum shows a broad and intense absorption in the 1500–400 cm−1 region, typical of short hydrogen bonds. In the Raman spectrum the broad absorption is absent. Linear correlations between the experimental 13C NMR chemical shifts (δexp) in D2O and the GIAO/B3LYP calculated magnetic isotropic shielding tensors (σcal), δexp = a + bσcal, are analyzed.