Structural and vibrational spectral investigations of melaminium maleate monohydrate by FTIR, FT-Raman and quantum chemical calculations

The structural investigations of the molecular complex of melamine with maleic acid, namely melaminium maleate monohydrate have been carried out by quantum chemical methods in addition to FTIR, FT-Raman and far-infrared spectral studies. The quantum chemical studies were performed with DFT (B3LYP) method using 6-31G**, cc-pVDZ and 6-311++G** basis sets to determine the energy, structural and thermodynamic parameters of melaminium maleate monohydrate. The hydrogen atom from maleic acid was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak OH⋯O and NH⋯O hydrogen bonds shows notable vibrational effects.

Graphical abstractThe structural investigations of the molecular complex of melamine with maleic acid, namely melaminium maleate monohydrate have been carried out by quantum chemical methods in addition to FTIR, FT-Raman and far-infrared spectral studies. The hydrogen atom from maleic acid was transferred to themelamine molecule giving the singly protonated melaminium cation. The observed internal C5N3C2 angle (119.3°) at protanated N-atom is significantly greater than other two ring angles C5N6C7 (115.1°) and C7N1C2 (115.7°). The ability of ions to form spontaneous three-dimensional structure through weak OH⋯O and NH⋯O hydrogen bonds shows notable vibrational effects.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► FTIR, FT-Raman and DFT studies of melaminium meleate monohydrate were carried out. ► The protonation of melamine affect the side chain C2N8, C5N11 and C7N14 bonds. ► The melaminium cations are joined together by maleate anions and water molecules by NH⋯O and OH⋯O type hydrogen bonds. ► The electrostatic potential of the complex is in the range +6.54e × 10−2 to −6.54e × 10−2. ► The protonation of triazine ring cause dramatic changes in the frequencies of the ring.