OHO hydrogen bond and electrostatic interactions in a complex of pyridine betaine with phenylacetic acid studied by X-ray diffraction, FTIR spectroscopy and PM3, DFT calculations

Crystalline complex of pyridine betaine with phenylacetic acid (PBPHA) has been prepared and characterized by single-crystal X-ray analysis, FTIR spectroscopy, PM3 and DFT calculations. The crystals are monoclinic, space group P2(1)/c, with a = 15.902(2), b = 6.2866(8), c = 16.005(2) Angstrom, beta = 119.18(1)degrees and with one complex molecule in the asymmetric unit. The molecule of phenylacetic acid is linked to pyridine betaine by a strong, asymmetric hydrogen bond (O . . .O 2.521(2) Angstrom). A characteristic motif of the crystal packing is a tetrameric unit consisting of two inversion-related molecules of PBPHA. The tetrameric unit is stabilized by EDA interaction between the pyridine and phenyl rings and by C-H . . .O contacts. The FTIR spectrum shows a broad absorption in the 2800-800 cm(-1) range with a maximum at about 1300 cm(-1) due to the antisymmetric mode of hydrogen bond and a complex absorption in the carbonyl-carboxylate region. Both PM3 and DFT calculations predict a slightly longer hydrogen bond and di different relative orientation of the aromatic rings than those in the crystal. (C) 2000 Elsevier Science B.V. All rights reserved.