Unusual hydrogen-bonding aggregation in 4-amino-1-(2-carboxyethyl)pyridinium bromide hemihydrate

The structure of 4-amino-1-(2-carboxyethyl)pyridinium bromide hemihydrate (1), has been studied by X-ray diffraction, B3LYP/6-311++G(d,p) calculations, FTIR and NMR spectroscopies. The crystals are monoclinic, space group P21/c. In the crystal a unique association of carboxyl group of 4-amino-1-(2-carboxyethyl)pyridinium cation is present, where one of two symmetry-independent groups is H-bonded to another one forming a centrosymmetric dimer, and the second symmetry-independent group is H-bonded to a water molecule. The crystal is built of chains, formed by the Br−H2O–cation–Br—cation–cation–Br—cation–H2OBr− links, bifurcated at Br− anions and water molecules, each involved in three hydrogen bonds. The probable assignments of the anharmonic experimental vibrational frequencies of the compound are based on the calculated frequencies in vacuum. Correlations between the experimental 13C and 1H NMR chemical shifts (δexp) and the GIAO/B3LYP/6-311++G(d,p) calculated magnetic isotropic shielding constant (σcalc) in D2O, δexp = a + b·σcalc, are reported.