Structure and vibrational spectra of the solid complex of betaine-sulphuric acid monohydrate

Abstract

The crystal structure of betaine-sulphuric acid monohydrate has been determined by X-ray diffraction as a monoclinic species of space group P21a, with a = 14.108(1) Å, b = 11.702(2) Å, c = 6.520(3) Å, β = 101.00(3) and Z = 4. The crystal comprises hydrogen-bonded units containing two bisulphate ions and two water molecules linked in a ring, with a protonated betaine molecule attached to each of the bisulphate ions. Neighbouring units are linked by a hydrogen bond between a bisulphate ion and a water molecule. Powder FT-IR and Raman spectra were measured, and an assignment of the observed bands to vibrations of the hydrogen bonds and internal vibrations of the bisulphate ion and the betaine molecules is proposed. No evidence was found for any spectral changes in the vicinity of the phase transition previously reported at 253.7 K.