Crystal structure and vibrational spectra of melaminium 2,5-dinitrophenolate monohydrate: FT-IR, FT-Raman and quantum chemical calculations

A new organic–organic salt, melaminium 2,5-dinitrophenolate monohydrate has been synthesized and characterized by X-ray diffraction, FT-IR and FT-Raman spectroscopies for the protiated and deuteriated crystals. The title compound crystallizes in triclinic system P1¯ (Ci in Schönflies notation). Its vibrational spectra have been discussed on the basis on quantum chemical density functional theory (DFT) calculations using B3LYP/6-31G(d,p) approach. Acidic proton of the phenol group was transferred to the melamine molecule giving the singly protonated melaminium cation. The ability of ions to form spontaneous three-dimensional structure through weak O–H⋯O and N–H⋯O hydrogen bonds is fully utilized. These hydrogen bonds give notable vibrational effects.