Molecular structure, hydrogen bonding and spectroscopic properties of the complex of piperidine-4-carboxylic acid with chloroacetic acid

Complex of piperidine-4-carboxylic acid with chloroacetic acid has been studied by X-ray diffraction, FTIR, Raman, 1H and 13C NMR spectroscopy and B3LYP/6-31G(d,p) calculations. In crystal the piperidine ring is protonated and adopts a chair conformation with the COOH group in the equatorial position. The COO− group of chloroacetate unit is engaged in three hydrogen bonds: O(1)–H(1)···O(3) of 2.604(2) Å, N(1)–H(12)···O(3) of 2.753(2) Å and N(1)–H(11)···O(4) of 2.760(2) Å. According to the B3LYP calculations the isolated complexes both in vacuum and H2O solution have cyclic structures. In vacuum the molecules are connected by two H-bonds: the COOH group of chloroacetic acid is engaged with piperidine-4-carboxylic acid, one with the nitrogen atom, O(4)–H···N(1) of 2.658 Å and the second with carboxyl group, O(1)–H···O(3) of 2.860 Å. In water solution piperidine-4-carboxylic acid is protonated and forms two hydrogen bonds with the chloroacetate unit: N(1)–H···O(4) of 2.690 Å and O(1)–H···O(3) of 2.611 Å. Powder FTIR spectra of the complex and its deuterated analogue are consistent with the X-ray structure. Correlations between the experimental 1H and 13C chemical shifts of the complex investigated and the GIAO/B3LYP/6-31G(d,p) calculated magnetic isotropic shielding tensors (σcalc) in vacuum and within the conductor-like screening continuum solvation model (COSMO) in H2O, δexp = a + b σcalc, are reported.