Polarised IR and Raman spectra of monoglycine nitrate single crystal

Abstract

Polarised Raman spectra of the monoglycine (monoglycinium) nitrate (hereafter MGN) single crystal are reported. Additionally, the polarised specular reflection spectra for the (1 0 0) single crystal sample (E|| Y( b) and E|| Z( c)) were measured in the region 3600–80 cm −1. The spectra of the imaginary parts of the refractive indices are computed by the Kramers–Kronig transformation (Opus). The polarised spectra are discussed with respect to the diffraction crystal structure and recent literature data on normal co-ordinate analysis for the glycinium cation ( +NH 3CH 2COOH). The stretching vibrations of the NH 3 + groups are explained by considering their hydrogen bonds. The intensity of the Raman bands arising from the stretching vibrations of the CH 2 group are explained assuming that each C H bond stretches independently. This finding is unusual and suggests that the C(2) H(5) bond is involved in the hydrogen bonding (improper hydrogen bond). The deformation vibrations of the CH 2 group are explained assuming scissoring, twisting, wagging and rocking type of vibrations. The band at 871 cm −1 exhibits the CC stretching character of the CCN skeleton, whereas the band at ca. 1050 cm −1 shows the ν aCCN character. The stretching νOH vibrations of the C O H⋯O hydrogen bond gives rise to a band at ca. 3087 cm −1, clearly seen in the Y( xx) Z Raman spectrum. Its γOH mode appears at 896 cm −1. The δOH vibration is coupled to other vibrations, although the IR band at ca. 1375 (E|| Y) likely arises from this mode. It was impossible to define a character of the glycinium cations deformation vibrations giving rise to the bands observed in between 680 and 490 cm −1, on the basis of their polarisation properties. The polarisation properties of the internal modes of the nitrate ions are discussed.