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Keywords:

  • bis(L-proline) hydrogen nitrate;
  • bis(L-proline) hydrogen perchlorate;
  • pyrrolidine ring;
  • factor group analysis;
  • hydrogen bonding;
  • group wavenumbers

Abstract

FT-IR and FT-Raman spectra were recorded for bis(L-proline) hydrogen nitrate and bis(L-proline) hydrogen perchlorate crystals. The wavenumber assignments have been made for the proline functional groups, viz. COOH, COO, C[BOND]N[BOND]C[BOND]C[BOND]C ring, [BOND][NH2]+, [BOND](CH2)[BOND], C[BOND]C[BOND]N and C[BOND]H. In both crystals, two proline residues share one proton and become monoprotonated. The observed bands show that in both compounds one of the proline residues is in the zwitterionic form while the other is in the cationic form. In the two compounds under investigation, the vibrational bands for the proline residues are almost similar. In the pyrrolidine ring there exists a protonated imino group [NH2]+ and CH2 groups showing the aliphatic nature of the proline in the inorganic acid environments. The symmetry of the nitrate group is not affected. Hydrogen-bonding network leads to the shifting of bands corresponding to several stretching and deformation modes. In bis(L-proline) hydrogen perchlorate, the identification of bands due to ClO2 group reveals that the symmetry of ClO4 anion is possibly reduced to C2v. Copyright © 2005 John Wiley & Sons, Ltd.