CRYSTAL-STRUCTURE AND SPECTROSCOPIC ANALYSIS OF MELAMINE HYDROBROMIDE - EVIDENCE FOR ISO-MELAMINE CATIONS AND CHARGE-TRANSFER COMPLEXES IN THE SOLID-STATE

The crystal structure and vibrational analyses of melamine hydrobromide by FTIR and FT-Raman spectra, are presented. The crystallographic data show pi-electron delocalization towards the amino substituents with ring nitrogen protonation in the solid state. Additionally, the presence of intermolecular hydrogen bonding interactions occurring between amino substituents and ring nitrogen lone-pairs gives rise to charge-transfer complexes, as demonstrated by UV-VIS reflectance in the solid state. FTIR and FT-Raman spectra allow the assignments of the vibrational modes in melamine hydrobromide by comparison with the corresponding deuteriated molecules, and show the existence of iso-melamine cations in the solid state.