Molecular structure and vibrational spectra of Bis(melaminium) terephthalate dihydrate: A DFT computational study

The experimental and theoretical vibrational spectra of Bis(melaminium) terephthalate dihydrate were studied. The Fourier transform infrared (FT-IR) spectra of the Bis(melaminium) terephthalate dihydrate and its deuterated analogue were recorded in the solid phase. The molecular geometry and vibrational frequencies of Bis(melaminium) terephthalate dihydrate in the ground state have been calculated by using the density functional method (B3LYP) with 6-31++G(d,p) basis set. The results of the optimized molecular structure are presented and compared with the experimental X-ray diffraction. The molecule contains the weak hydrogen bonds of NH⋯O, NH⋯N and OH⋯O types, and those bonds are calculated with DFT method. In addition, molecular electrostatic potential, frontier molecular orbitals and natural bond orbital analysis of the title compound were investigated by theoretical calculations. The lack of the second harmonic generation (SHG) confirms the presence of macroscopic center of inversion.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The vibrational spectra of the Bis(melaminium) terephthalate dihydrate were examined. ► The DFT theoretical results were compared experimental results. ► Thermodynamic properties at different temperatures were calculated. ► The NBO, MEP and HOMO–LUMO are also analysed.