The study of crystal structures and vibrational spectra of inorganic salts of 2,4-diaminopyrimidine

Six novel salts of 2,4-diaminopyrimidine were prepared and studied by X-ray single-crystal structure analysis and vibrational spectroscopy. All but one of the title compounds, i.e. (2,4-diaminopyrimidine) 2,4-diaminopyrimidinium perchlorate, 2,4-diaminopyrimidinium nitrate, 2,4-diaminopyrimidinium perchlorate, bis(2,4-diaminopyrimidinium) hydrogen phosphate tetrahydrate and bis(2,4-diaminopyrimidinium) selenate dihydrate, crystallize in the triclinic system with the centrosymmetric space group P1¯ while the crystals of the remaining compound - 2,4-diaminopyrimidinium chloride hemihydrate - belong to the monoclinic system (space group C2/c). All the crystal structures contain the characteristic graph set motif R22(8) with N-H… N hydrogen bonds. This graph set motif can be formed by one of three possible arrangements of a pair of 2,4-diaminopyrimidinium cations and all these arrangements have been observed in the title structures. The title salts were also investigated by vibrational spectroscopy (FTIR and FT Raman). The presented interpretation of the vibrational spectra is based on DFT calculations of 2,4-diaminopyrimidine molecule and 2,4-diaminopyrimidinium cation.