Structure and polarized infrared and Raman spectra of the solid complex of betaine and maleic acid (1:1)

Abstract

Crystals of betaine maleic acid (BHM) of the formula [(CH 3) 3N +CH 2COOH]·[HCOOCHCHCOO −] are monoclinic, space group P 1 n , with a = 6.138(3), b = 10.831(4), c = 17.244(5) A ̊ , β = 92.85(4)° and Z = 4. The betaine cation is linked to the maleic monoanion by a strong intermolecular O ⋯ O hydrogen bond of length 2.527(3) Å forming a “structure unit”. The hydrogen maleate anion forms a ring structure containing a short, very asymmetric intramolecular hydrogen bond: O ⋯ O = 2.429(3), OH = 1.04(4), H ⋯ O = 1.39(4) A ̊ . The polarized infrared and Raman spectra of the BHM single crystal have been measured at room temperature. The hydrogen bond modes and the internal vibrations of the maleate anion and betaine cation are discussed in relation to the crystal structure. A broad absorption was observed due to the antisymmetric stretching mode of both short hydrogen bonds, but it could not distinguish features pertaining to the intramolecular and intermolecular hydrogen bonds, respectively.