Structure and spectroscopic properties of bis(1-carboxyethyl-3-aminopyridinium) hydrobromide monohydrate

The structure of bis(1-carboxyethyl-3-aminopyridinium) hydrobromide monohydrate, (3-NH2PB2)2HBr⋅H2O (1), has been studied by X-ray diffraction, B3LYP/6-311G(d,p) calculations, FTIR and NMR spectroscopy and calorimetric measurements. The compound crystallizes in orthorhombic, space group Pbca. The Br anion and water molecules are positionally disordered so that Br(1) and O(1w) are located at the same positions with the same average occupations and they form O(1w)H⋯Br bonded zigzag chains along [1 0 0], with the Br⋯O(1w)⋯Br and O(1w)⋯Br⋯O(1w) angles equal 121.0(3)°. These chains are connected to the O(1)⋯H(1)⋯O(11) bonded cations through NH⋯Br and NH⋯O(1w) bonds. A pair of 3-NH2PB2 molecules is bridged by a short symmetric O(1)·H·O(11) hydrogen bond of 2.462(6) Ǻ. The FTIR spectrum of (1) shows a broad and intense absorption in the 1500-400 cm−1 range, similar to that in the spectra of type A acid salts of carboxylic acids and other 2:1 betaine complexes with mineral acids. The assignment of the anharmonic experimental solid-state vibrational frequencies of the compound investigated is proposed based on the second-derivative spectrum (d2). Correlations between the experimental 13C and 1H NMR chemical shifts (δexp) and the GIAO/B3LYP/6-311G(d,p) calculated magnetic isotropic shielding constants (σcal) in DMSO-d6, δexp = a + b·σcalc, are reported.