FT-Raman, FT-IR, UV spectra and DFT and ab initio calculations on monomeric and dimeric structures of 3,5-pyridinedicarboxylic acid

The FT-IR and FT-Raman spectra of 3,5-pyridinedicarboxylic acid (dinicotinic acid, C7H5NO4) in the solid phase were recorded. The fundamental vibrational wavenumbers, intensities of vibrational bands and the optimized geometrical parameters of the compound are evaluated using HF and DFT (B3LYP) methods with 6-311G(d) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The computed dimer parameters also show agreement with experimental data. The complete assignments were performed on the basis of the total energy distribution (TED). Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. UV–visible spectrum of the compound was recorded in the region 200–400 nm and the electronic properties HOMO and LUMO energies were measured by time-dependent TD-DFT approach. Thermodynamic properties (heat capacity, entropy and enthalpy) of the title compound at different temperatures were calculated.