X-ray, phase transition, IR and Raman studies of the solid complex of bis(pyridine betaine)-sulphuric acid

Crystals of bis(pyridine betaine)-sulphuric acid complex are monoclinic, space group C2/c, a = 12.464(2) Angstrom, b = 10.771(2) Angstrom, c = 12.541(3) Angstrom, beta = 101.20(3)degrees. The SO42- group is located on a twofold axis and forms an U-shaped system, bridged by two short and identical H-bonds, with two protonated betaine molecules (O...O distances 2.472(7) Angstrom and O-H...O angle 165 degrees). The solid state FTIR spectrum of the complex shows a carbonyl band at ca. 1722 cm(-1) and a broad absorption extending from ca. 2800 down to 400 cm(-1). On deuteration the broad absorption shifts slightly to lower frequencies and the isotope ratio of the centre of gravity of the total absorption in the 2800-400 cm(-1) region is v'(H)/v'(D) = 1.07 The frequencies of the narrow skeletal vibration from the broad absorption were subtracted using second-derivative spectroscopy. The I and II order phase transitions were found by DSC method. (C) 1997 Elsevier Science B.V.